THE TRYPANOSOME OF NAGANA 813 



the time of the death of the animal they number as many as the red cells : 

 in other animals they are not so numerous. 



Immunity. Laveran has shown that human serum has a specific action 

 on infected animals. When human serum (1-2 c.c. for a rat weighing 200 

 grams) is inoculated sub-cutaneously into an infected rat or mouse, the 

 parasites rapidly disappear from the blood : but they reappear after 4r-S 

 days. By repeating the injections the life of the infected animals can be 

 considerably prolonged, though a permanent cure is never obtained. 



Human serum is feebly prophylactic. Thus, when inoculated at the same 

 time as the trypanosomes it will sometimes prevent infection but the animal 

 is not immunized : if inoculated 24 hours before the virus infection is 

 delayed. The serum of all the lower animals (monkeys, etc.) is without any 

 action. 



Some species of animals (cattle, goats and sheep for example) often recover 

 from an attack of Nagana, and they are then immune to the disease and 

 their blood has prophylactic properties against Tr. brucei (Laveran). 



Schilling and Koch have devised a means of vaccinating cattle. The method 

 consists in using a trypanosome which has been passed two or three times through 

 dogs or through dogs and rats alternately : the passage virus sets up usually a mild 

 infection in cattle and the animals become immune, but occasionally a severe infec- 

 tion is produced. To avoid this Schilling increased the number of passages, first 

 passing the trypanosome seven times through dogs and rats alternately, then 

 eighteen to twenty times through dogs only. It is stated that bovine animals resist 

 inoculation with this passage virus very well and that their serum exhibits bac- 

 tericidal properties for the trypanosome : but the efficiency of the method has yet 

 to be confirmed. It is inapplicable in the case of horses since these animals 

 succumb to the inoculation of the passage virus. 



Martini succeeded in keeping alive for a long time two asses which had resisted 

 inoculation with a trypanosome after it had been passed through mice and which 

 had been subsequently inoculated five times intra-venously. The serum of these 

 asses, which ultimately died, proved to be prophylactic for mice. At the time of 

 death their blood was infective for the dog. 



Laveran and Mesnil have tried, but unsuccessfully, to produce immunity 

 by inoculating animals with an attenuated virus (attenuation being effected 

 by age, heat, cold, mixing with toluidine blue, etc.). The incubation period 

 following the inoculation of the attenuated trypanosomes is longer than 

 normal, but once the disease develops it runs its ordinary course. 



African Trypanosomiases related to Nagana. 



Animals in Africa are subject to many trypanosome infections. The parasites in 

 these diseases are all more or less like T. brucei and may be divided into several 

 species. 



Trypanosoma soudanense. Szewczyk, and Rennes have observed an epizootic 

 among horses in the French Sudan (Mai de la Zousfana) running a chronic course 

 and having as its causal agent a trypanosome (Trypanosoma soudanense) similar to 

 that of Surra (Laveran). 



The same parasite is responsible for the disease of dromedaries observed by 

 Cazalbou in the French Sudan and known as Mbori or " the fly disease," and of 

 the disease of dromedaries described by Ed. and Et. Sergent in Algeria and known 

 as El Debab. 1 



Trypanosoma dimorphon, studied by Button and Todd in Gambia, which infects 

 mules, cattle, sheep and horses in French Guinea, Dahomey, the Congo and Senegal 

 is also closely related to the trypanosome of Nagana. 



Trypanosoma congolense (Brodden) has been found in the Congo in sheep and 

 asses in the neighbourhood of Leopoldville, and in cattle, dogs and sheep near 

 Brazzaville. It is very closely related to T. dimorphon. 



1 [El Debab, the fly or horse fly.] 



