Clonal variation in paramecium. Heterogeneity within clones of identical serotypes.

Clones of genetically uniform paramecia differ in the extent to which they retain the antigenic type of a common ancestor. Some are faithful and are considered stable. Others are unstable. Apparently there are two kinds of "unstable" clones. One is composed of cells all of which tend to produce subclones with some cells which have transformed to new serotypes. Other "unstable" clones apparently are really composed of two or more kinds of cells, each of which tends to yield subclones which are made up almost exclusively of cells of one serotype, although some of these subclones are not of the original serotype. Support for the existence of such heterogeneous unstable clones is presented, and several possible mechanisms to account for their existence are discussed.

Real-time measurement of microvascular dimensions using digital cross-correlation image processing.

A real-time automatic digital image-processing algorithm was developed for measuring microvascular dimensions. Using video microscopic images of the vasculature, the video images are digitized and analyzed using contrast enhancement, frame averaging, and pattern recognition, rather than edge detection. Performance of the algorithm was evaluated for second- and third-order vessels surrounded by the complex interfering features of in vivo skeletal muscle. Graded diameter changes and vasomotion were induced with pharmacological agents. Data obtained by auto-tracking agreed with data obtained by traditional manual methods of measurement. These findings indicate that a pattern recognition algorithm based on cross-correlation analysis provides a highly accurate method for real-time automatic tracking of microvessel diameters.