CLASSIFICATION OF THE MAIN SUBDIVISIONS 473 



4. Finally, the Guarnieri's body breaks up, and the cell becomes 

 full of initial corpuscles, which divide up in their turn into numerous 

 elementary corpuscles, and the cycle is complete. 



An interesting problem, from both the medical and biological points of 

 view, is that of the relation of the organism of vaccinia (cow-pox) to that of 

 variola (small-pox). It is well known that an inoculation with vaccine-lymph 

 (vaccination) produces a transitory local disturbance which confers partial 

 immunity against infection with variola. It does not seem to be quite clear 

 whether the organisms of vaccinia and variola are to be regarded as two 

 distinct species or as two phases or conditions of the same species of or- 

 ganism ; the latter is the view of Calkins, as stated above. Manson has 

 suggested (Brit. Med. Journ., 1905, ii., p. 1263) that the relationship between 

 the organisms of vaccinia and variola may be similar to that between 

 Leislimania tropica, of Oriental Sore, and L. donovani, of Kala-azar. No 

 evidence has been brought forward as yet, however, to show that an infection 

 with Oriental Sore confers any immunity against Kala-azar. 



The Chlamydozoa have been most studied in those cases where 

 their power of producing disease has forced them upon the atten- 

 tion of medical investigators, but it is not to be supposed that as a 

 group of organisms they occur solely as parasites of higher animals. 

 It is probable that they are of widespread occurrence, and that the 

 peculiar nuclear parasite of Amoeba, known as Nucleophaga, Dan- 

 geard, for instance, should be referred to the Chlamydozoa (com- 

 pare Schepotieff, 269), and perhaps also the similar parasite of 

 Paramecium described by Calkins under the name Caryoryctes, 

 No Chlamydozoa are known, however, to occur as free-living, non- 

 parasitic organisms, but this circumstance may be due to their 

 extreme minuteness ; the species known owe their detection to the 

 disturbances they' cause in their hosts. Finally, it must be men- 

 tioned that the parasitic theory of cancer, sometimes thought to be 

 long since defunct, has been revived recently by Awerinzew (907), 

 who is of opinion that cancer is caused by intranuclear parasites of 

 the nature of Chlamydozoa. 



Such, briefly summarized, is the present position of the problem. 

 Future research must decide the truth or falsity of one or the 

 other of the solutions that have been advocated. It only remains 

 to discuss briefly the nature of the Chlamydozoa, if the interpreta- 

 tion of Prowazek and his adherents be accepted. According to 

 Prowazek and Lipschiitz (913), the Chlamydozoa belong neither to 

 the Bacteria nor to the Protozoa. Hartmann (909), however, seems 

 to consider that their development and their characteristic mode of 

 division are Protozoan characteristics. The " development," how- 

 ever, seems to consist of little, if anything, more than growth in size. 

 As "elementary corpuscles" they are smaller, as "initial bodies" 

 larger. The dumb-bell-shaped figure seen in division may mean 



