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SCIENCE 



[N. S. Vol. XXXIV. No. 



the intra-nuclear centrosome divides first. 

 In all cases the kinetic center appears to 

 be formed from chromatin, or at least 

 from nuclear material and seems to be 

 made up of a special kind of nucleoplasm. 

 Frequently, as in Trypanosoma, Trypano- 

 ■plasnia and allied forms, the kinetic center 

 emerges from the nucleus as in Heliozoa, 

 but is accompanied by a small amount of 

 chromatin thus forming a second nucleus 

 which Woodcock has aptly named the 

 kinetonucleus. Such double nuclei, which, 

 it may be pointed out, are in no way homol- 

 ogous with the dimorphic nuclei of in- 

 fusoria, have led Hartmann, Nagier, 

 Prowazek and some others to form a 

 special group of protozoa termed the Bi- 

 nuclearia. The point of view leading to 

 this artificial group has been ably criticized 

 by Dobell. 



Fourth, as to chromidia. Goldschmidt 

 and others of the Munich school have in- 

 terpreted a number of indeterminate stnic- 

 tures of tissue cells as chromidia or gran- 

 ules of chromatin discharged from the 

 nucleus. Waiving the question for the 

 present as to whether such objects are 

 chromidia or chondriosomes of unknown 

 origin, there is no doubt whatever that 

 chromidia of nuclear origin occur in pro- 

 tozoa and play a most important role in 

 their vital processes. In rhizopods espe- 

 cially, chromidia are formed during, or 

 prior to, the period of maturity, by nu- 

 clear secretion, nuclear dissolution or nu- 

 clear fragmentation, the granules becom- 

 ing individually, or after fusion, the nuclei 

 of conjugating gametes. It thus becomes 

 possible to speak of a special germ plasm 

 in protozoa as distinct from somatic 

 plasm. Such chromidia are to be distin- 

 guished from the products of nuclear 

 degeneration which occur under abnormal 

 conditions of feeding or environment and 

 which are more analogous to nuclear de- 



generation and granulation-tissue forma- 

 tion in higher animals. 



There remain many lines of research in 

 protozoan cytology, especially in the direc- 

 tion of maturation and fertilization phe- 

 nomena, only a few forms having been ade- 

 quately studied. The enigmatical third 

 division in maturation has evidently some 

 connection with sex, since this division is 

 heteropolar in Didinium, Paramecium 

 caudatum and P. hursaria, the smaller nu- 

 cleus migrating, the other stationary, dur- 

 ing conjugation. Splendid results lie at 

 the end of patient study in this line of re- 

 search. 



II. THE PATHOGENIC SIDE 



The development of this branch of proto- 

 zoa study was so rapid and so spectacular 

 and seemed to arise so unexpectedly out of a 

 clear field, that many investigators, espe- 

 cially pathologists and other medical men, 

 are inclined to regard it as constituting the 

 whole of protozoology. Up to 1890 only 

 two human diseases were suspected of be- 

 ing caused by protozoa. These were 

 dysentery and malaria. To-day more than 

 fifteen human diseases are known or sus- 

 pected to be of protozoan origin. 



Parasitic amcebai were first observed in 

 the human intestine in victims of dysentery 

 by Losch in 1875. He had no hesitation 

 in claiming them to be the cause of dysen- 

 tery and named the organism Amoeba coli. 

 Other pathologists, however, soon found 

 similar organisms in the intestines of 

 normal men and Losch 's claim was dis- 

 credited. Councilman and Lafleur in 

 1891 found two types of amoebse, one of 

 which — A. coli — was considered a harm- 

 less commensal, the other, which they 

 called Amoeba dysenteries, they claimed to 

 be the cause of tropical dysentery. Casa- 

 grandi and Barbagallo in 1897 were the 

 firet to actually prove that the coli form is 



