Transmission 559 



actual culture was made chiefly in the water of condensation 

 collected at the bottom of obliquely congealed media. 



Laveran and Mesnil found that when blood containing 

 Trypanosoma gambiense was mixed with salt solution or 

 horse-serum, the trypanosomes remain alive for five or six 

 days at the temperature of the laboratory. They live much 

 longer in tubes of rabbit's blood and agar, sometimes as long 

 as nineteen days, and during this time many dividing forms 

 but no rosettes were observed. But subcultures failed, and 

 eventually the original culture died out. 



Reproduction. Multiplication takes place by binary 

 division, the line of cleavage being longitudinal. The cen- 

 trosome and nucleus divide, then the flagellum divides longi- 

 tudinally, and finally the protoplasm divides. 



In addition to this simple longitudinal fusion, the trypan- 

 osomes seem to possess a sexual mode of reproduction. When 

 the well-stained organisms are carefully studied, it is possible 

 to divide them into three groups those that are peculiarly 

 slender, those that are peculiarly broad, and those of ordinary 

 breadth. The fact that conjugation takes place between the 

 first two has led to the opinion that they represent the male 

 and female gametocytes respectively, while the others are 

 asexual. All forms multiply by fission, and conjugation 

 between the gametes is observed to take place only in the 

 body of the invertebrate host. It has not yet been accurately 

 followed in the case of Trypanosoma gambiense, but there is 

 no reason to think that the organism differs in its method of 

 reproduction from Trypanosoma lewisi. Prowazek found 

 that when rat blood containing the latter organism was 

 taken into the stomach of the rat louse, Hematopinus spinu- 

 losus, the male trypanosome enters the female near the 

 micronucleus and the various parts of the two individuals 

 become fused. A non-flagellate ookinete results, and, after 

 passing through a spindle-shaped gregarine-like stage, can 

 develop into an immature trypanosome-like form in the cells 

 of the intestinal epithelium, after which the parasite is 

 thought to enter the general body cavity, and, migrating to 

 the pharynx, enter the proboscis, through which it is trans- 

 mitted to a fresh host. 



Transmission. It is well known that the disease does 

 not spread from person to person. In the days when African 

 negroes were imported into America as slaves the disease 

 often reached our shores, and though freshly arrived negroes 



