APPENDIX. 335 



recent studies, believe that the bodies above mentioned are 

 protozoa. Segmentation of the bodies is described, result- 

 ing in the formation of spore-like 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. 



YELLOW FEVER. 



It has already been indicated (page 160) 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. 



As malaria and some other diseases transmitted by mosquitoes are due 

 to protozoa, careful search has been made for protozoa in yellow fever. 

 Examinations of the blood of individuals having yellow fever have been 

 without result. Recently Parker, Beyer and Pothier have studied speci- 

 mens of Stegomyia fed on such blood. They claim to have found that 

 these mosquitoes became infected with a protozoon parasite, a portion 

 of whose cycle was worked out. 1 Ordinary mosquitoes did not contain 

 the parasite. Blood-serum from a case of yellow fever was filtered 

 through a Berkenfeld filter and injected into two healthy subjects; one 

 subject developed yellow fever and the other did not. The interpreta- 

 tion of these results in connection \vith the experiments of Reed and 

 Carroll (page 161) is not at present clear. 



Trypanosomes. A number of species of Trypanosoma have been de- 

 scribed, which produce diseases in the lower animals; recently one has 

 been stated to be the cause of disease in man. 2 The trypanosoma is a 

 protozoon belonging to the flagellata. It is of an elongated spindle- 

 shaped form, with a nucleus, and has a flagellum at one end, which 

 extends along a thin edge, called the undulating membrane. It is ac- 

 tively motile. It occurs in the blood, between, but not in, the blood- 

 corpuscles. Its length is two to several times the diameter of a red 

 corpuscle. Members of this genus are the cause of surra (a fatal dis- 



1 Marine Hospital Service. Yellow Fever Institute, Bulletin No. 13, 

 March, 1903. 



2 For a full description of the life history and classification of Trypan- 

 osoma see Salmon and Stiles, Emergency Report on Surra. U. S. 

 Bureau Animal Industry, Bulletin No. 42, 1902. See also Francis, 

 Marine Hospital Service, Hygienic Laboratory, Bulletin No. n, 1903. 



