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0.8/* in length. Preer (1948a, 1950) further observed that the kappa 

 particles contain desoxyribonucleic acid and vary in form (rod-like or 

 spherical), size and number in different races of killers, and that an 

 increase, reduction or destructon of the kappas, as determined by 

 indirect methods, was correlated with the observed number of the 



Fig. 102. Photomicrographs of Paramecium, aurelia, stained with 

 Giemsa's stain (Sonneborn). a, a killer with a number of kappa particles 

 in the cytoplasm; b, a sensitive without kappa particles, a few dark- 

 stained bodies near the posterior end being bacteria in a food vacuole. 



stained particles. As to the suggestion that the kappa particles may 

 be viruses, symbionts (Altenberg, 1948), etc., the reader is referred 

 to Sonneborn (1946, 1950). 



The application of antigen-antibody reactions to free-living Pro- 

 tozoa began some forty years ago. Bernheimer and Harrison (1940, 

 1941) pointed out the antigenic dissimilarity of three species of 

 Paramecium in which the members of a clone differ widely in their 



