236 GARY N. CALKINS. 



period of sexual union is imminent. For example, in the case of 

 the ordinary forms of Anurba it is remarkable that sexual proc- 

 esses have never been observed, although the engulfing of 

 one individual by another has been interpreted as a conjuga- 

 tion phenomenon. One series of forms has recently come to 

 my notice which seems to indicate a sexual process. The or- 

 dinary form of A. protcus, usually has but a single nucleus, but 

 in one culture in my laboratory after a long series of uninucleated 

 forms a culture appeared in which the individuals were in various 

 phases of encystment or in nuclear fragmentation immediately 

 prior to encystment. It was found that the single primary 

 nucleus divides by mitosis ; that these divide again and so on 

 until as many as seventy large nuclei may fill the body of the 

 amoeba. In some cases before this number is reached the larger 

 nuclei begin to break down into large granules which become 

 distributed throughout the cell appearing exactly like the idio- 

 chromidium of Difflngia, Arcclla or Centropyxis. All but one of 

 the primary nuclei are finally disposed of in this way, that one re- 

 maining unused even in the final encysted stage. In this final 

 stage the cyst is filled with many reproductive bodies, which from 

 analogy with other rhizopods I interpreted as gametes. 



Not only is chromidium formation important in determining 

 the phase of development of a given form, but it may also be of 

 the greatest assistance in proving the protozoon nature of ques- 

 tionable structures found in certain diseased tissues. An interest- 

 ing example has recently come up in connection with the organ- 

 ism of rabies. This organism, under the name of the Negri 

 bodies, has been looked upon with great suspicion by biologists 

 and pathologists alike, and from its general staining reaction and 

 from its ordinary vesiculated appearance it has been more fre- 

 quently passed by as an artifact or secretion or degeneration 

 product, than considered as an organism. But during the season 

 just passed, Dr. A. W. Williams, of New York, working with a 

 different method from that ordinarily employed, was able to prove 

 that what appear usually as vesicles in these bodies are in reality 

 substances which take a characteristic nucleus stain with the 

 Giemsa method, and she shows that the Negri bodies are 

 amoeboid cells with nuclei in different stages of chromidium 



