Agricultural origins: centers and noncenters.

I propose the theory that agriculture originated independently in three different areas and that, in each case, there was a system composed of a center of origin and a noncenter, in which activities of domestication were dispersed over a span of 5,000 to 10,000 kilometers. One system includes a definable Near East center and a noncenter in Africa; another system includes a North Chinese center and a noncenter in Southeast Asia and the South Pacific; the third system includes a Mesoamerican center and a South American noncenter. There are suggestions that, in each case, the center and noncenter interact with each other. Crops did not necessarily originate in centers (in any conventional concept of the term), nor did agriculture necessarily develop in a geographical "center."

Distribution of wild wheats and barley.

If we accept the evidence at face value, we are led to conclude that emmer was probably domesticated in the upper Jordan watershed and that einkorn was domesticated in southeast Turkey. Barley could have been domesticated almost anywhere within the arc bordering the fertile crescent. All three cereals may well have been harvested in the wild state throughout their regions of adaptation long before actual farming began. The primary habitats for barley, however, are not the same as those for the wheats. Wild barley is more xerophytic and extends farther downslope and into the steppes and deserts along the wadis. It seems likely that, while all three early cereals were domesticated within an are flanking the fertile crescent, each was domesticated in a different subregion of the zone. Lest anyone should be led to think the problem is solved, we wish to close with a caveat. Domestication may not have taken place where the wild cereals were most abundant. Why should anyone cultivate a cereal where natural stands are as dense as a cultivated field? If wild cereal grasses can be harvested in unlimited quantities, why should anyone bother to till the soil and plant the seed? We suspect that we shall find, when the full story is unfolded, that here and there harvesting of wild cereals lingered on long after some people had learned to farm, and that farming itself may have orig inated in areas adjacent to, rather than in, the regions of greatest abundance of wild cereals. We need far more specific information on the climate during incipient domestication and many more carefully conducted excavations of sites in the appropriate time range. The problem is far from solved, but some knowledge of the present distribution of the wild forms should be helpful.

Chromosome pairing within genomes in maize-Tripsacum hybrids.

When the ten chromosomes of maize were inserted inlto a polyploid (2n = 72) Tripsacum dactyloides background they formed up to five pairs at meiosis. Two plants that each contained 36 Tripsacum and 14 maize chromosomes were deprived from the F(1) of maize x Tripsacum. Chromo. somes of these plants frequently formed 25 bivalents, 18 between Tripsacum chromosomes and seven between maize chromosomes. Maize chromosomes could be distinguished from Tripsacum chromosomes on the basis of size. The withint-genome pairing is probably induced by the genetic background.

Tripsacum-maize interaction: a novel cytogenetic system.

The genera Zea and Tripsacum cross readily when they are not isolated by gametophytic barriers, and it has been postulated that intergeneric introgression played a role in the evolution of maize. The basic x = 9 Tripsacum and x = 10 Zea genomes have little cytological affinity for each other in hybrids that combine 10 Zea with 18 Tripsacum chromosomes. However, one to four Tripsacum chromosomes sometimes associate with Zea chromosomes in hybrids between Z. mays (2n = 20) and T. dactyloides (2n = 72). These hybrids with 10 Zea and 36 Tripsacum chromosomes frequently produce functional female gametes with 36 Tripsacum chromosomes only. When they are pollinated with maize, their offspring again have 36 Tripsacum and 10 maize chromosomes, but the Tripsacum genome is contaminated with maize genetic material. In these individuals, intergenome pairing is the rule, and when they are pollinated with maize, their offspring have 36 Tripsacum and 10, 12, 14, 16, 18, or 20 Zea chromosomes. Plants with 36 Tripsacum and 20 Zea chromosomes behave cytologically as alloploids, although the Tripsacum genome is contimated with maize, and one basic maize genome is contaminated with with Tripsacum genetic material. When they are pollinated with maize, offspring with 18 Tripsacum and 20 Zea chromosome are obtained. Further successive backcrosses with maize selectively eliminate Tripsacum chromosomes, and eventually plants with 2n = 20 Zea chromosomes are recovered. Many of these maize plants are highly "tripsacoid." Strong gametophytic selection for essentially pure Zea gametes, however, eliminates all obvious traces of Tripsacum morphology within a relatively few generations.

Pathways of genetic transfer from Tripsacum to Zea mays.

The cytogenetic interactions in maize x Tripsacum hybrid derivatives can be remarkably complex. The number of viable, somewhat female fertile chromosome combinations is astonishing. Fifty-four different combinations are listed in this paper, and others are certainly possible. In successive backcrosses to maize, chromosome numbers scale both up and down with ease, sometimes stabilizing for a few generations via apomixis, but in most cases finally generate balanced maize genomes and emerge as recovered maize. The maize, however, can produce strange and unusual phenotypes as a result of genetic transfers from Tripsacum. Highly tripsacoid maize lines with 2n = 20 chromosomes were recovered in pathways where the maize genome had first contaminated the Tripsacum genome in early backcross generations. In other pathways interaction of the two genomes is rare. Dominant resistances to six maize diseases were found in BC(8) populations.

Endoscopic therapy for patients with a post-operative biliary leak.

Twenty-three patients with a post-operative biliary leak were treated by various endoscopic methods and results were analyzed. Leaks occurred at the cystic duct in 13 patients, at the common duct in 6 patients, and at an anomalous branch of the right hepatic duct in 4 patients. Treatments included sphincterotomy alone (4 patients), stent alone (6 patients), sphincterotomy and stent (12 patients), and sphincterotomy and nasobiliary drainage catheter (1 patient). Five patients also had supplemental percutaneous catheter drainage of a biloma. All treatments were completed successfully in the absence of major morbidity, and permanent closure of the leak occurred in 100% of cases. Endoscopic therapy for patients with a post-operative biliary leak is safe and effective and should be recommended before surgical re-exploration.

A prospective, controlled analysis of endoscopic cytotechniques for diagnosis of malignant biliary strictures.

We prospectively collected brushings and bile for cytology in 30 consecutive patients with bile duct strictures (17 malignant, 13 benign) who were assessed by endoscopic retrograde cholangiography. When appropriate, the cellular debris on stents that were removed from individuals who were managed with these devices was evaluated for malignant cells as well. Our aim was to assess the value of these endoscopic cytotechniques for making a diagnosis of obstructing cancer of the biliary tract. A cumulative total of 78 specimens were obtained. Overall, sensitivity was highest for stent (36%) and brush (33%) cytology, compared with results obtained from bile (6%). If the results for all methods are combined, 47% of patients with cancer (eight of 17) could be diagnosed by one or more cytological technique. There were no false-positive results (specificity, 100%). Our results show that brush and stent cytology are nearly equivalent for detecting cancer, but because a diagnosis is delayed until the endoprosthesis is removed (mean 3.4 months), the brush technique is preferred. Results for bile cytology are marginal. Specificity for these cytotechniques is high; therefore, a positive result by any method is sufficient evidence for cancer, and other invasive diagnostic procedures are unnecessary.

Emergency endoscopic retrograde cholangiopancreatography in critically ill patients.

BACKGROUND: The aim of this study was to assess the frequency, indications, yield, and outcome of emergency endoscopic retrograde cholangiopancreatography (ERCP) in critically ill patients. METHODS: Records of all intensive care unit patients undergoing emergency ERCP were reviewed over a 40-month period. Indications, findings, therapeutic interventions, and survival were analyzed. Those requiring mechanical ventilation at the time of ERCP were in group A and those who did not were in group B. RESULTS: Of 1781 ERCPs, 32 (1.80%) were performed on intensive care unit patients. Fifteen patients belonged to group A (46.87%) and 17 (53.13%) to group B. The common bile duct was the duct of interest in 30 patients (94%) and was cannulated in 97%. Indications included possible biliary sepsis (68.75%), gallstone pancreatitis, and jaundice (12.5% each). The most common finding was choledocholithiasis (34%), followed by failure to fill the cystic duct (16%) and common bile duct stricture (9%). A normal examination was present in 18.75% of cases. Endoscopic therapy was required in 66.6% of patients in group A and 70.5% of group B. The overall 30-day mortality was 25% (33% for group A and 17.6% for group B) and not related to the ERCP. CONCLUSIONS: Two percent of all ERCPs performed were on intensive care unit patients (47% requiring mechanical ventilation) primarily to evaluate for possible biliary sepsis. Technical success was not compromised by mechanical ventilation. Therapeutic intervention was required in more than two thirds of patients and the overall 30-day mortality was 25%.

Endoscopic retrograde wire-guided brush cytology for diagnosis of patients with malignant obstruction of the bile duct.

A brush was adapted for use over a guide wire to facilitate reliable acquisition of cytological specimens from tight and potentially malignant strictures encountered during ERCP. Cells collected in this manner were assessed for abnormalities indicative of cancer. We have called this technique endoscopic retrograde wire-guided brush cytology (ERWBC). Thirty-nine strictures (24 malignant, 15 benign) in 34 patients were brushed. There were no complications, and all specimens were adequate for evaluation. Sixty percent of patients with cancer were diagnosed by ERWBC. Sensitivity was highest for cholangiocarcinoma (100%), intermediate for pancreatic cancer (60%), and lowest for patients with biliary obstruction due to metastatic disease (22%). There were no false-positive results (specificity, 100%). The positive and negative predictive values were 100% and 58%, respectively, and accuracy for the test was 72%. Collection of cytological specimens using a brush with a wire guide is effective especially for diagnosis of cholangiocarcinoma. A positive result is sufficient evidence for malignancy, and other invasive diagnostic tests are unnecessary. We recommend ERWBC for brushing all strictures of unknown cause during ERCP in an effort to make a diagnosis of cancer.