384 NAGANA 
“Dourine and mal de caderas can not be transmitted to cattle. 
“In regions where mal de caderas exists cattle do not die of surra- 
‘We have no reason to believe that trypanosoma show the same 
irregularities of virulence as bacteria, so that the different forms of 
the disease may be said to be produced by different degrees of virul- 
ence in the same trypanosoma. On the contrary, during our four 
years of experimentations, the latter have shown a constant virul- 
ence.” 
The fourth reason which he considers decisive is based on the 
morphological differences in the parasites. 
Voges concludes by saying, “I think these four proofs are entirely 
sufficient to establish for all time the difference between surra and 
dourine as well as between surra and mal de caderas.”” Laveran and 
Mesnil give extensive consideration to the differences between surra 
and nagana. A summary of their considerations is appended. 
“The same animals are susceptible to both diseases—the horse, ass, 
mule, goat, sheep, cow, camel, dog, cat, monkey (long-tailed macayo), 
rabbit, guinea-pig, and rat. 
“In the horse the course of the disease is the same, whether surra 
or nagana. The animal dies at the same time, in 30 days on the 
average. In inoculation cases the period of incubation is the same, 
and the same symptoms and lesions supervene. 
“The other equides, the goat, sheep and dog, die of the two diseases 
in the same length of time and with similar symptoms and lesions. 
“Rabbits, guinea-pigs and rats succumb to the infection in a like 
manner. 
“Cows rarely survive nagana, and they rarely die from surra. 
They become emaciated with surra but recover in health and a subse- 
quent inoculation does no harm. This is a marked difference between. 
them but it may be explained when further experiments are made.” 
Laveran and Mesnil believe that the paralysis of the posterior 
extremities, a marked symptom in mal de caderas, is less marked in 
surra and nagana, although they believe the three affections very 
closely related. Dourine differs from the other three in two distinct 
points: (1) The morphology of the parasite is different. (2) In dourine 
contagion by coition seems to be the only natural mode of infection. 
Much additional investigation will be necessary before the question 
of either the identity or the non-identity of these affections can be 
positively determined. As these diseases are not liable to become of 
great economic importance in this country, further discussion of the 
voluminous literature seems unnecessary. 
