700 



SCIENCE 



[N. S. Vol. XXV. No. 644 



longed consecutive passage but readily in- 

 fect susceptible animals. 



We have shown, however, that cultures 

 of T. brucei can be attenuated by exposure 

 for about two days at 34° C. By repeated 

 injections of cultures thus treated, attempts 

 have been made to immunize rats and 

 guinea pigs against T. hrucei, but thus far 

 these have been but partially successful. 

 That is to say, there has been at most a 

 survival of a few days of the treated as 

 compared with the untreated animals. The 

 failure to immunize with such cultures is 

 attributable in part to the excessive sus- 

 ceptibility, of the animals employed, to in- 

 fection with T. hrucei, and in part to the 

 existence of a negative phase following the 

 injections. It is desirable to repeat these 

 experiments with less susceptible animals. 



In view of the fact that rats invariably 

 recover, some soon, others late, from infec- 

 tion with T. lewisi and the further fact 

 that rich cultures of this organism are 

 readily obtainable, it is evident that this 

 species is well adapted for studies on im- 

 munity. Up to the present time it has not 

 been satisfactorily shown that trypano- 

 somes elaborate toxins or that they confer 

 immunity by means of soluble or intracel- 

 lular products. The latter problem was 

 approached by means of plasmolyzed cul- 

 tures. To effect solution of the trypan- 

 osomal cells the cultures were taken up in 

 distilled water and dialyzed in coUodium 

 sacs. Usually after one or two hours of 

 such dialysis in distilled water the trypano- 

 somes completely disappear and the intra- 

 cellular matter apparently passes into solu- 

 tion. 



By means of such plasmolyzed cultures 

 it has been shown that rats which receive 

 three or more injections, on alternate days, 

 on subsequent inoculation with a minimal 

 infective dose of fresh trypanosomal blood 

 from a rat do not become infected, whereas 



controls are positive. With such solutions 

 it is possible to hyperimmunize rata so that 

 0.5 c.c. of the immune rat blood protects 

 against a simultaneous and separate injec- 

 tion of the infective blood. 



Protection is seemingly obtained against 

 T. lewisi by simultaneous and separate in- 

 jection of the infective blood and plas- 

 molyzed culture, followed twenty-four 

 hours later by a second injection of the 

 latter. Repeated injections of too large a 

 quantity of the plasmolyzed culture and at 

 too short an interval leads to a negative 

 phase, the presence of which is indicated by 

 the unusually early appearance of trypano- 

 somes in the blood after inoculation with 

 the virus. 



Inasmuch as it may be said that the 

 plasmolyzed material does not represent a 

 true solution, a series of experiments were 

 made with the filtered (Berkefeld) plas- 

 molyzed liquid. While these experiments 

 go to show that immunity can probably be 

 induced by such filtered soluble products 

 they are not as decisive as they should be 

 and for that reason will have to be re- 

 peated. The chief reason for this uncer- 

 tain result is the rather frequent failure 

 of the control rats to develop infection. 

 Although young rats (50-80 grams) were 

 used to guard against previous infection 

 with trypanosomes it is certain that a large 

 percentage of the rats, as purchased on the 

 market, have acquired an immunity against 

 T. lewisi. That the immunity encountered 

 is really acquired and not natural is shown 

 by the fact that we have many times iso- 

 lated T. levjisi, by means of the cultivation 

 method, from rats which on repeated ex- 

 amination were found to be free from para- 

 sites and hence were supposed to be normal. 



Program of the Second Session, 

 December 28, 1906 

 (Joint meeting of Section K and the 

 Society of American Bacteriologists.) 



