49 



Somewhat related to Trypanosoma dimorphon, but more uniform in 



size, is the Trypanosoma congolense ; according to the immunity test it 



must be differentiated from the former. Two goats which recovered 



from an injection were used in Laveran's experiments.* Sub-inoculation 



into smaller animals proved the sterility of the recovered goats' blood. 



The animals were reinjected with the same strain ; again they both 



showed a slight infection. Further inoculation however did not cause 



any more infection ; the animals had acquired immunity. The two 



recovered goats were now inoculated with Trypanosoma dimorphon. 



Both animals contracted a typical infection from which one died and 



the other was still alive on the date of pubhcation (November, 1908). 



Conclusion. — Recovery from a first attack of Trypanosoma congolense 



did not convey a complete immunity. A second infection with the same 



strain proved successful. Subsequent recovery increased this immunity. 



The blood of immune animals was sterile. Immunity against 



Trypanosoma congolense did not protect against Trypanosoma 



dimorphon. 



Serum Experiments. — The experiments of Laveran,! Mesnil, J Martin, § 



Kleine,|| and Mollers,|| and of others with trypanosomes can be resumed 



as foUowsf : — 



(1) Serum of animals suffering or recovered from an advanced 

 trypanosomiasis has distinct preventive qualities. When homologous 

 serum and virus were mixed before injection no infection took place ; 

 independently injected the results varied. In experiments of hetero- 

 logous mixtures of serum, and virus no preventive actions were noticed. 



(2) The serum of an animal suffering from advanced trypanosomiasis 

 may be active against the trypanosomes of the same blood from which 

 the serum was derived (Kleine and MoUer). 



(3) Animals which supply a serum with preventive properties may 

 retain the infection in the blood, and the serum of such blood has no 

 preventive action on the corresponding trypanosomes, even if such 

 trypanosomes have passed through a succession of animals (Mesnil and 

 Brimont). 



Summary. 



Animals may recover from trypanosomiasis and then prove to be 

 immune against the strain with which they have been infected ; it is an 

 exception that the same strain again causes an infection, but the different 

 strains may cause reinfection. 



Animals may be immune and their blood remain infective or they 

 may be immune and the blood becomes sterile. 



Serum of infected or recovered animals has slight protective pro- 

 perties. 



* Contrib. a FEtude de Trvp. congolense : Aun. dc Tlnst. Past., t. XXII, Nov., IflOS. 

 tComptes Eendus, t. CXLII, p. 1482. 

 i Ann. de I'lnst. Past., t. X. 

 § Zeitsch fur Hyg. t. L., 4/4/05. 

 II Zeitsch fur Hya" t. LTI., 1906. 



