Quantum multifractality as a probe of phase space in the Dicke model.

We study the multifractal behavior of coherent states projected in the energy eigenbasis of the spin-boson Dicke Hamiltonian, a paradigmatic model describing the collective interaction between a single bosonic mode and a set of two-level systems. By examining the linear approximation and parabolic correction to the mass exponents, we find ergodic and multifractal coherent states and show that they reflect details of the structure of the classical phase space, including chaos, regularity, and features of localization. The analysis of multifractality stands as a sensitive tool to detect changes and structures in phase space, complementary to classical tools to investigate it. We also address the difficulties involved in the multifractal analyses of systems with unbounded Hilbert spaces.

Quantum localization measures in phase space.

Measuring the degree of localization of quantum states in phase space is essential for the description of the dynamics and equilibration of quantum systems, but this topic is far from being understood. There is no unique way to measure localization, and individual measures can reflect different aspects of the same quantum state. Here we present a general scheme to define localization in measure spaces, which is based on what we call Rényi occupations, from which any measure of localization can be derived. We apply this scheme to the four-dimensional unbounded phase space of the interacting spin-boson Dicke model. In particular, we make a detailed comparison of two localization measures based on the Husimi function in the regime where the model is chaotic, namely, one that projects the Husimi function over the finite phase space of the spin and another that uses the Husimi function defined over classical energy shells. We elucidate the origin of their differences, showing that in unbounded spaces the definition of maximal delocalization requires a bounded reference subspace, with different selections leading to contextual answers.

The effects of mercaptoethanol and of peritoneal macrophages on the antibody-forming capacity of nonadherent mouse spleen cells in vitro.

Nonadherent mouse spleen cells exhibited poor viability and little or no capacity to form antibodies to sheep red cells in the Mishell-Dutton culture system. Viability and antibody-forming capacity could be restored by addition to these cultures of low concentrations of mercaptoethanol (10(-4)-10(-5)M), or by addition of appropriate numbers of mouse peritoneal macrophages. Macrophage concentrations lower than optimal resulted in lower lymphoid cell viability and correspondingly fewer plaque-forming cells, whereas excess macrophages resulted in marked inhibition of antibody formation despite good viability of the lymphocytes. Restoration of the nonadherent cells with mercaptoethanol was thus much simpler and more reproducible than it was with macrophages; furthermore, the number of plaque-forming cells developed in cultures restored with mercaptoethanol was approximately fourfold higher than it was in cultures restored with optimal numbers of macrophages. In the presence of mercaptoethanol, the plaque-forming capacity of the nonadherent spleen cells was not increased when small numbers of macrophages were added to the system, nor was it decreased when the few macrophages present in the nonadherent cells were further reduced or eliminated. Excess macrophages inhibited antibody formation in the cultures containing mercaptoethanol as they did in control cultures. Optimal restoration of plaque-forming capacity to the nonadherent spleen cells with mercaptoethanol required the reducing agent to be present throughout the 4 or 5 day culture period. Addition of mercaptoethanol 1 or more days after initiation of culture, or transfer of the cells to a medium free of mercaptoethanol before completion of the culture resulted in a reduction in the numbers of plaque-forming cells. The results suggest that mouse lymphoid cells do not require macrophages in order to form antibodies to sheep red cells in vitro, provided mercaptoethanol is present in the culture medium. The mechanism of action of mercaptoethanol under these conditions is not completely clear, but one of its effects is to promote the viability of lymphoid cells in the cultures.

The interaction between Toxoplasma gondii and mammalian cells. II. The absence of lysosomal fusion with phagocytic vacuoles containing living parasites.

Electron microscope methods have been used to study delivery of macrophage primary or secondary lysosomal contents to phagocytic vacuoles containing living or dead toxoplasmas. Secondary lysosomes were labeled by culturing the cells in colloidal thorium dioxide (thorotrast) or in ferritin. Acid phosphatase cytochemistry was employed for detection of primary as well as secondary lysosomal constituents. These various lysosomal labels were present in nearly all vacuoles containing toxoplasmas killed with glutaraldehyde, or in vacuoles containing those parasites undergoing degeneration 1 hr after the uptake of living toxoplasmas. In contrast, at times ranging from 1 to 20 hr after infection, no vacuoles containing morphologically normal, apparently viable toxoplasmas were thorotrast or ferritin positive, and only rarely did these vacuoles react for acid phosphatase. In many instances vacuoles containing viable toxoplasmas and no lysosomal markers were situated in the same cell nearby to vacuoles containing degenerating toxoplasmas and lysosomal constituents, thus indicating that the determinants of lysosomal fusion were operating locally in the immediate vicinity of the phagocytic vacuole, and not operating to influence general cell function. Thus, some toxoplasmas are able to prevent the delivery of lysosomal contents, and apparently the phagocytic vacuole provides for these parasites a sheltered microenvironment ideal for their growth. Morphologic evidence indicated that living toxoplasmas altered the phagocytic vacuolar membrane in macrophages, fibroblasts, and HeLa cells. Within minutes after phagocytosis, the vacuole became surrounded by closely apposed strips of endoplasmic reticulum and mitochondria; somewhat later, microvillous protrusions of the membrane into the vacuole were seen. These morphologic features of phagocytic vacuoles containing living toxoplasmas may be of importance in relation to the absence of lysosomal fusion, or they may serve some function in protecting the host cell or in nourishing the parasite.

Assessment in vitro of immunity against Toxoplasma gondii.

Studies have been made on humoral and cellular immune respones in mice immunized with an attenuated strain of Toxoplasma gondii. Heat-inactivated antitoxoplasma serum did not cause morphologic changes in the organisms, but did markedly influence their interactions with host cells. Toxoplasma exposed to antibody were no longer capable of entering fibroblasts or HeLa cells. They were readily engulfed by macrophages, but the antibody treatment strikingly altered the intracellular fate of the parasites leading to killing and digestion of the toxoplasmas in phagolysosomes. Addition of antitoxoplasma antibody immediately after infection of macrophages in vitro had no effect on intracellular multiplication of the organism. The division time of virulent toxoplasmas in mouse peritoneal macrophages in vitro was markedly prolonged in cells from immunized mice. During the first 2-3 mo after immunization, the macrophages harvested from the peritoneal cavity demonstrated this cellular immunity directly; thereafter exposure of the macrophages to immune lymphocytes and toxoplasma antigen, or to supernates from such an interaction was required for induction of the maximal capacity to inhibit growth of toxoplasmas. Induction of the alternation in macrophages by the lymphocyte product was detectable in 6 h and maximal at 18-24 h. Cultivation in vitro of macrophages from immunized animals for periods longer than 48 h rendered the cells nonresponsive to the immune lymphocyte-toxoplasma product. Macrophages from the peritoneal cavities of normal, nonimmunized mice were also incapable of developing the capacity to inhibit growth of toxoplasmas in response to this product. The nonresponsiveness of normal macrophages, or of macrophages cultured for several days in vitro was not changed by exposure of the cells to antitoxoplasma serum.

Macrophage plasma membranes. I. Isolation and studies on protein components.

Plasma membranes have been isolated from pure populations of rabbit alveolar macrophages which were swollen in water, fixed briefly with glutaraldehyde, disrupted by Dounce homogenization, and separated by sucrose gradient centrifugation. The recovered membranes exhibited good structural preservation and enzymatic activity; both morphologic and biochemical evidence indicated a high degree of purity (>90%) of the membrane preparation. Interiorized plasma membranes were also prepared without exposure to glutaraldehyde from phagocytic vacuoles recovered from alveolar macrophages which had ingested large numbers of polystyrene spheres. These membranes were contaminated with lysosomal constituents, but they were nevertheless of value for comparison to the "pure" membranes isolated by the glutaraldehyde procedure. Acrylamide gel electrophoresis of the solubilized plasma membranes and phagolysosomal membranes revealed similar protein patterns, with seven to nine individual components ranging in molecular weight from 70,000 to 140,000. The two most rapidly migrating components gave positive reactions for lipid as well as protein. A band containing carbohydrate was detected near the origin of the plasma membrane gels. Antisera were made by injecting guinea pigs with the purified rabbit alveolar macrophage plasma membranes. Gel diffusion and immunoelectrophoretic study of these antisera established the presence of rabbit immunoglobulin G and of one or two other antigenic constituents in the membrane preparation.

The interaction in vitro of Mycoplasma pulmonis with mouse peritoneal macrophages and L-cells.

Methods have been devised for establishing infection in vitro of mouse macrophages and fibroblasts with Mycoplasma pulmonis. The mycoplasmas attached to the cells and under appropriate cultural conditions grew into a lawn of microorganisms covering most of the cell surface. The mycoplasmas grew abundantly on fibroblasts cultured in minimal essential medium containing 20% fetal calf serum; supplementation of this medium with heart infusion broth was necessary to obtain similar growth on macrophages. The infection of these cells appeared to be essentially an extracellular process; only rarely were partially degraded mycoplasmas seen with phagocytic vacuoles. The addition to heavily infected macrophage cultures of low concentrations of anti-mycoplasma antibody stimulated rapid, massive phagocytosis of the surface microorganisms. In sharp contrast, the same antiserum had no discernable effect on the mycoplasma-fibroblast relationship. The antibody effect in the macrophage system was apparently a direct opsonic one rather than an indirect result of microbial killing, since the mycoplasmas in macrophage or fibroblast cultures incorporated labelled thymidine into DNA after the addition of antiserum to the medium. The phagocytic event and the subsequent fate of the mycoplasmas were studied in detail after the addition of antibody to the macrophage cultures. Phase-contrast cinemicrophotography revealed membrane ruffles surrounding the surface mycoplasmas and disappearance from view of the organisms; 10-30 min later translucent grapelike clusters were seen in large phagocytic vacuoles. On electronmicroscopic study the surface mycoplasmas were surrounded by pincers-like projections of the macrophage. Numerous mycoplasmas were seen in phagocytic vacuoles; in the early minutes after the addition of antibody the intracellular mycoplasmas appeared normal, but within 2 hr they appeared partially degraded with a central electron-lucent area and electron-opaque deposits at the microbial cell margin. 24 hr after the addition of antiserum, digestion of the mycoplasmas was nearly complete; the cells appeared normal except for large residual bodies composed of amorphous moderately dense material and increased lipid deposits. Degradation of mycoplasmas within macrophages was also studied using infected cultures in which the mycoplasmas, but not the macrophages, had incorporated tritiated thymidine into DNA. The appearance of large amounts of acid-soluble radiolabel after phagocytosis stimulated by antibody confirmed the degradation of the intracellular mycoplasmas.

Macrophage plasma membrane. II. Studies on synthesis and turnover of protein constituents.

Rabbit alveolar macrophages were incubated in vitro with radioactive protein precursors. Plasma membranes were isolated from these cells, dissolved in phenol-urea-acetic acid, and separated by acrylamide gel electrophoresis. (3)H-leucine was rapidly incorporated into membrane protein. The rate of labeling with (3)H-leucine was markedly different from one protein band to another, indicating heterogeneous or multistep synthesis and assembly of proteins in the alveolar macrophage plasma membrane. Cells incubated with (3)H-choline incorporated this compound into membrane lecithin. On gel electrophoresis the label derived from choline was located in the two bands migrating most rapidly towards the cathode. Studies on cells incubated with (3)H-glucosamine revealed incorporation of label into two protein bands, one located near the origin and the other migrating rapidly towards the cathode. The in vitro techniques were also employed for pulse-chase studies to gain information on rate of turnover of macrophage plasma membrane proteins. This turnover rate was rapid, with a half-life of approximately 8 hr. The radioactivity disappeared from the several protein bands at the same rate, suggesting bulk removal of membrane rather than catabolism of the individual proteins in situ. Endocytosis seems a likely mechanism to account for a major part of the plasma membrane removal. Studies on the protein components of phagolysosomal membranes from cells which had been labeled with (3)H-leucine revealed the presence of all of the major labeled protein bands characteristic of the plasma membrane except one, thus confirming the bulk interiorization of large segments or units of plasma membrane by endocytic processes.

The interaction between Toxoplasma gondii and mammalian cells. I. Mechanism of entry and intracellular fate of the parasite.

Macrophage, fibroblast, and HeLa cell cultures have been infected with Toxoplasma gondii, and observations have been made on parasite entry and fate. A special procedure was devised for studying the entry of toxoplasmas by electron microscopy. Toxoplasmas were centrifuged onto the cells in the cold; fixation 1-3 min after warming yielded specimens showing numerous examples of parasites in the process of entering cells. The mechanism of entry into macrophages, fibroblasts, and HeLa cells was in all cases by phagocytosis. Micropseudopods were extended by the cells to envelop the attached parasites in a typical phagocytic vacuole. Apparently the toxoplasmas stimulated this response of HeLa cells and fibroblasts, cell types not usually phagocytic. No instance was seen of penetration of toxoplasmas through the cell membrane, or of parasites located free in the cytoplasm. Essentially all of the toxoplasmas that entered HeLa cells divided with a generation time of 9 hr; the parasites formed large rosettes situated in vacuoles, eventually leading to host cell rupture. Macrophages took in larger numbers of toxoplasmas than did HeLa cells, but approximately half of the parasites inside of macrophages degenerated within a few hours. The surviving toxoplasmas in macrophages divided every 8 hr, forming rosettes and eventually rupturing the cells.

Leukocyte locomotion and chemotaxis. New methods for evaluation, and demonstration of a cell-derived chemotactic factor.

Polymorphonuclear leukocyte (PMN) locomotion and chemotaxis have been evaluated by direct microscopic observation of individual cells in thin slide-cover slip preparations, and also by observations on populations of cells migrating into a Millipore filter. The direct microscopic method used the polarity of the locomoting PMNs (broad, advancing lamellipodium and knoblike constriction at the rear) to record the direction of movement. The Boyden chamber Millipore assay was made more reliable by following the front of cells advancing into the filter, rather than counting the number of cells on the lower filter surface. Special modifications of the Millipore assay were necessary in order to distinguish between influences on rate of locomotion and true chemotaxis. In both systems the results indicate that under certain conditions leukocytes, and in particular PMNs, release into the medium a factor stimulating locomotion and exerting chemotactic action on PMNs in the vicinity. This cell-derived factor appears not to require serum factors for its release or action.

The relationship of polymorphonuclear leukocytes to infertility in uteri containing foreign bodies.

A chronic infiltration of polymorphonuclear leukocytes was invariably found in the infertile regions of uteri containing foreign bodies in conventional rats, germfree rats, mice, and rabbits. Polymorphonuclear leukocytes were never found in the fertile regions of these uteri. A foreign body in the uterus of the rat, and probably also the mouse, was associated with a bacterial infection which spread the inflammatory response throughout the horn containing the foreign body, and in the mouse occasionally into the control horn as well. No bacteria could be cultured from the rabbit uterine horn containing a foreign body. In the germfree rat, both the infiltration of polymorphonuclear leukocytes into the uterus and fertility were significantly different from that observed in the conventional rat. Whereas in the conventional rat the inflammation and infertility extended along the entire length of the uterine horn containing a small foreign body, in the germfree rat the inflammation and infertility were closely correlated to the position of the foreign body. As judged by measurements of lysozyme in the uterine lumens of rats and rabbits, polymorphonuclear leukocytes released their contents into solution in the uterine lumen. It is concluded that some substance derived from polymorphonuclear leukocytes may exert toxic effects on fertilized ova or on spermatozoa and thus be responsible for the infertility of uteri containing foreign bodies.

The in vitro differentiation of mononuclear phagocytes. IV. The ultrastructure of macrophage differentiation in the peritoneal cavity and in culture.

The structure of unstimulated mouse peritoneal phagocytes has been examined by electron microscopy and compared to cells obtained from the inflamed peritoneum and from cultures maintained in vitro. The unstimulated cell resembles the blood monocyte and contains a moderate amount of rough surfaced endoplasmic reticulum, a small but well defined Golgi apparatus and a few, small, electron-opaque granules in the cytoplasm. During in vitro cultivation there are marked changes in cell ultrastructure. Most prominent is the formation of large electron-opaque granules, some of which have a complex matrix containing both electron-opaque and lucent vesicles. In addition, there is an increase in size of the Golgi apparatus with the appearance of new lamellae and tiny, smooth surfaced vesicles. With continued cultivation, large lipid droplets are found in apposition to the rough endoplasmic reticulum. The formation and size of electron-opaque granules as well as the enlargement of the Golgi region is stimulated by high concentrations of serum in the medium. Cells obtained from the peritoneal cavity of lipopolysaccharide stimulated animals demonstrated changes in ultrastructure similar to those seen in cells cultured in vitro.

The in vitro differentiation of mononuclear phagocytes. V. The formation of macrophage lysosomes.

A combined morphological, autoradiographic, and cytochemical study at the electron microscope level has been directed towards the formation of electron-opaque granules of cultured macrophages. Labeling of the membrane-bound vesicular structures of pinocytic origin was accomplished with colloidal gold. The initial uptake of gold occurred within micropinocytic vesicles. These electron-lucent vesicles subsequently fused with and discharged their contents into larger pinocytic vacuoles. Colloidal gold was homogeneously distributed in the large pinosomes. In contrast, gold was initially deposited in the periphery of preformed dense granules indicating that these structures were also in constant interaction with the external environment. Colloidal gold was not observed within the cisternae of the endoplasmic reticulum nor within the saccules or vesicles of the Golgi apparatus. There were, however, many small, gold-free vesicles, indistinguishable from Golgi vesicles, which were preferentially aligned about and appeared to fuse with the large pinosomes. The intracellular flow of leucine-H(3)-labeled protein was followed by electron microscopic autoradiography. After a 15 min pulse of labeled amino acid there was initial labeling of the rough endoplasmic reticulum. Subsequently, much of the label appeared in the Golgi complex. At still later time periods the cytoplasmic dense granules contained the majority of the isotope. Acid phosphatase activity was localized to the dense granules and in the majority of cells to the Golgi apparatus. It is suggested that hydrolytic enzymes are initially synthesized in the endoplasmic reticulum and are then transferred to the Golgi apparatus. Here they are packaged into small Golgi vesicles which represent the primary lysosome of macrophages. The Golgi vesicles subsequently fuse with pinosomes, thereby discharging their hydrolases and forming digestive granules or secondary lysosomes.

Morphology and peroxidase cytochemistry of mouse promonocytes, monocytes, and macrophages.

Mouse promonocytes have been identified and studied in cultures of bone marrow cells. These cells have a diameter of 14-20 micro, and in stained preparations reveal a large, indented or folded nucleus, and basophilic, finely granular cytoplasm. The living promonocyte viewed by phase contrast shows additional features: nucleoli, small dense bodies, and vesicles in the cytoplasm adjacent to the nuclear hilus, and slight membrane ruffling. Prominent ultrastructural components of promonocytes include a well developed Golgi apparatus, small numbers of centrosomal granules and vacuoles, extensive ribosomal aggregates, and finger-like projections of the cell surface. Promonocytes engage in pinocytosis and phagocytosis, but they are less active in these functions than are peripheral blood monocytes of peritoneal macrophages. Promonocytes are positive for peroxidase, the reaction product being localized to granules most of which are centrally situated in the cell. Monocytes in blood or in inflammatory peritoneal exudates display much smaller numbers of peroxidase-positive granules, and various types of mature mouse macrophages are peroxidase negative.

Short-term adaptation to a simple motor task: a physiological process preserved in multiple sclerosis.

Short-term adaptation indicates the attenuation of the functional MRI (fMRI) response during repeated task execution. It is considered to be a physiological process, but it is unknown whether short-term adaptation changes significantly in patients with brain disorders, such as multiple sclerosis (MS). In order to investigate short-term adaptation during a repeated right-hand tapping task in both controls and in patients with MS, we analyzed the fMRI data collected in a large cohort of controls and MS patients who were recruited into a multi-centre European fMRI study. Four fMRI runs were acquired for each of the 55 controls and 56 MS patients at baseline and 33 controls and 26 MS patients at 1-year follow-up. The externally cued (1 Hz) right hand tapping movement was limited to 3 cm amplitude by using at all sites (7 at baseline and 6 at follow-up) identically manufactured wooden frames. No significant differences in cerebral activation were found between sites. Furthermore, our results showed linear response adaptation (i.e. reduced activation) from run 1 to run 4 (over a 25 minute period) in the primary motor area (contralateral more than ipsilateral), in the supplementary motor area and in the primary sensory cortex, sensory-motor cortex and cerebellum, bilaterally. This linear activation decay was the same in both control and patient groups, did not change between baseline and 1-year follow-up and was not influenced by the modest disease progression observed over 1 year. These findings confirm that the short-term adaptation to a simple motor task is a physiological process which is preserved in MS.

Ultrastructure of human leukocytes after simultaneous fixation with glutaraldehyde and osmium tetroxide and "postfixation" in uranyl acetate.

Human leukocytes in suspension or in monolayer cultures have been processed for electron microscopy by fixation in a freshly made cold mixture of glutaraldehyde and osmium tetroxide and by "postfixation" in uranyl acetate. Simultaneous exposure to glutaraldehyde and osmium tetroxide eliminates many of the shortcomings seen when either of these agents is used alone as the initial fixative. Specimens are processed to the stage of dehydration as single cell suspensions or as very small clumps to assure rapid penetration of fixatives and efficient washing. The technique is rapid and reproducible. Electron micrographs presented in this report illustrate the ultrastructural features of human white cells prepared by this method.

Cytoplasmic granule formation in myelocytes. An electron microscope radioautographic study on the mechanism of formation of cytoplasmic granules in rabbit heterophilic myelocytes.

The intracellular flow of tritiated lysine as revealed by electron microscope radioautography was studied in heterophilic myelocytes of rabbit marrow. Label over the Golgi complex rose to a maximum of 37% of total cytoplasmic grains 30 min after initial exposure to the tracer and fell to 11% after 3 to 4 hr of incubation. Coincident with decrease in label over the Golgi complex, grain counts over granules rose to 32% after 3 to 4 hr. The time sequence of incorporation and flow of tritiated lysine and the per cent distribution of label was similar in bone marrow myelocytes under in vivo and in vitro conditions. The results demonstrate a function of the Golgi complex in incorporating or packaging certain basic amino acids or proteins into cytoplasmic granules of heterophilic myelocytes.

Resolution of granules from rabbit heterophil leukocytes into distinct populations by zonal sedimentation.

Postnuclear supernates from homogenates of essentially pure rabbit heterophil leukocytes were fractionated by means of zonal differential centrifugation through a discontinuous sucrose gradient at various speeds. Three distinct groups of granules were characterized biochemically and morphologically. They were, in order of decreasing sedimentation coefficient: (a) Large, relatively dense granules, identified morphologically as the azurophil or primary granules, and containing essentially all of the myeloperoxidase activity of the preparations, about one-third of their lysozyme activity, and between 50 and 80% of their content in five acid hydrolases typically associated with lysosomes in other cells; (b) smaller, less dense granules, with the morphological appearance of the specific or secondary granules, and carrying most of the alkaline phosphatase and the remainder of the lysozyme activity of the preparations; (c) a second group of lysosome-like particles, associated with a morphologically heterogeneous fraction, and containing the remainder of the acid hydrolases, but little or no myeloperoxidase. When p-nitrophenyl phosphate was used instead of beta-glycerophosphate for the assay of acid phosphatase, only small proportions of the total activity accompanied the two main lysosomal bands, and considerable activity was found in a zone slightly retarded with respect to the slowly moving band of acid hydrolases.

Further biochemical and morphological studies of granule fractions from rabbit heterophil leukocytes.

Fractionation of rabbit heterophil leukocyte homogenates by isopycnic centrifugation as well as by zonal sedimentation has helped to characterize further the particulate components of these cells. Four classes have been identified: (A) Large (0.5-0.8 microm) and dense (1.26) azurophil or primary granules, containing all the myeloperoxidase, one-third of the lysozyme, and a major proportion of the lysosomal acid hydrolase activities of the cells. (B) Smaller (0.25-0.40 microm) and less dense (1.23) specific or secondary granules, containing 90% of the alkaline phosphatase and the remainder of the lysozyme activities, but very little if any acid hydrolases. (C) Particles of low density (1.20), containing the remainder of the lysosomal acid hydrolases. This fraction was heterogeneous, but showed abundant small rod- or dumbbell-shaped particles of moderate electron opacity, surrounded by a single membrane (tertiary granules?). The possible origin of these lysosomes from contaminating macrophages could not be ruled out but appeared unlikely. (D) Slowly sedimenting material of very low density (1.14), made up of large, empty vesicular membrane structures, and containing 10% of the alkaline phosphatase, and all of a thiol-dependent acid p-nitrophenyl phosphatase, an enzyme clearly different from the lysosomal acid phosphatase.

Studies on isolated membranes of azurophil and specific granules from rabbit polymorphonuclear leukocytes.

Membranes were prepared from rabbit polymorphonuclear leukocyte azurophil and specific granules separated by zonal differential centrifugation. The two types of granule membranes were quite similar in ultrastructural appearance, but they showed distinct differences in cholesterol-phospholipid ratios and in protein components demonstrable in polyacrylamide gels.