265 
The variation in virulence observed in the various strains of cattle, horse, and 
wild game trypanosomes found in the Congo is certainly not sufficient to suggest that 
more than one species of parasite was present. 
(3) Cross Inoculation. This method depends upon the belief 
that an animal which has acquired immunity* to one trypanosome can 
only be re-infected by a trypanosome of a different species. We 
believe that this method is open to many fallacies, especially because 
of the enormous difficulties of applying it. (a, b, c). 
(a) Experiments and observations of many authors show how 
extremely difficult it is to be certain that an animal has definitely 
recovered from a trypanosome infection. Cases of known infection 
often arise in which every means of demonstrating the parasite may 
fail.t 
(b) For the same reasons an animal may become infected without 
the infection being detected. 
(0 Our observations on Horse VI show that an animal may be 
twice infected by the same parasite. 
Laveran (17) infected a rat with T. gambiense which had recovered a year 
previously from a previous inoculation. Martin (15) records somew at sum 
experiences with a sheep and a goat. lie states that “ une mfime trypanosome peu 
revetir des virulences variables et une forme attenuee ne vaccine point con re 
forme exaltee,” basing this on the work of Koch and Martini. This complica es 
Hie question of the identity of any one trypanosome, and shows that additiona cau ion 
must be observed in placing too much reliance on the results of cross inocu a 10ns. 
k is altogether probable that the immunity in trypanosome infections is q ul e 
comparable to that seen in other protozoal diseases such as malaria and spiroc ae e 
infections, i.e., only a relatively active and not an absolute immunity is obtained. 
Although most authors, in describing a newly-discovered tiypano 
some, have found it difficult to say to what species their parasite 
belongs, the majority of the trypanosomes, other than 1 rypanosoma 
( qi<iperdiim, reported in domestic animals in Alrica, seem to be of the 
of either T. brucei or T. evansi. For example,Baleri as described 
°y ^azalbou, Jinja cattle disease found by the members of the Sleeping 
Sickness Commission in Uganda, Kidei as described by Sanders, 
Aino found in Somaliland, El Debab found by Sergent in camels in 
Algeria, Mbori affecting animals in French Soudan, Souma desen 
’°y Cazalbou, and the trypanosome described by Roger and Greftulhe 
'Horses in Algeria. _________ 
! n our hands the serum reactions dependent upon such immunity 
'^unreliable. . u 
jJrnk'' S P?‘ nt cannot be too strongly insisted upon. 11 ; ent^of trypano- 
St red by those engaged in experimental work on the treatment VP 
