336 MANUAL OF BACTERIOLOGY. 



recent studies, believe that the bodies above menti'oned are 

 protozoa. Segmentation of the bodies is described, result- 

 ing in the formation of spore-Uke bodies. The spore-like 

 bodies undergo a further or second cycle of development 

 within the nucleus. The second cycle also ends in segmenta- 

 tion. The two cycles were seen in small-pox; in vaccinia, 

 only the first or extranuclear bodies were observed. 





Fig. 105. — T-RYPANosuAiEs in the Blood op the Rai. Romanowsky 

 Stain. (X iooo.) 



yellow fevee. 



It has already been indicated (page 149) that the study of cases of yellow 

 fever has failed to prove that this disease is caused by bacteria. On the other 

 hand, evidence that it is transmitted by the mosquito, Stegomyia, has been 

 increasing. 



Trypanosomes. — A number of species of Trypanosoma have been described, 

 which produce diseases in the lower animals; recently one has been stated 

 to be the cause of disease in man.* The trypanosoma is a protozoon belong- 



* For a full description of the life history and classification of Trypanosoma 

 see Salmon and Stiles. Emergency Report on Surra. United States Bureau 

 Animal Industry. Bulletin No. 42. 1902. See also Francis. Marine Hos- 

 pital Service. Hygienic Laboratory. Bulletin No. 11. 1903. 



