428 TRYPANOSOMIASES 



ing the nature of these affections and the specific identity of 

 the exciting cause, render a differentiation or unification of 

 these most interesting diseases exceedingly difficult. Very 

 few investigators have had the opportunity of studying all of 

 them in their natural environment. The conclusion of Mus- 

 grave and Clegg in their recent report is worthy of considera- 

 tion. They say: "In summing up the whole matter it 

 appears to us, when we take into consideration the work done 

 by others and add our own results, that we are justified in 

 believing surra, nagana, mal de caderas, and probably dourine, 

 the same disease, and that all are caused by Tr. Evansii." 



Koch, who worked with surra and ?iagana, considered 

 the parasites and the resulting infections identical. Many 

 others have formed similar conclusions. Other investigators 

 such as Voges, L,averan and Mesnil and others maintain that 

 certain differences exist. The evidence is convincing that 

 dourine and mal de caderas are different in some respects from 

 the other two. Voges' reasons for this are : 



1. "Dourine and mal de caderas can not be transmitted 

 to cattle. 



2. "In regions where mal de caderas exists cattle do not 

 die of surra. 



3. "We Jiave no rea.son to believe that trypano.soma 

 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 virulence in the same trypanosoma. 

 On the contrary, during our four years of experimentations, 

 the latter have shown a constant virulence." 



4. 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 be- 

 tween su7'ra and dourine as well as between surra and )nal de 

 caderas.''' Laveran and Mesnil give extensive consideration to 

 the differences between surra and nagana. A summary of 

 their considerations is appended. 



