176 H. M. WOODCOCK. 



uncertain whether Nagana and Surra were distinct diseases or only two 

 varieties of the same. It may be here mentioned, in passing, that the 

 morphological difEerences between the organisms themselves are sometimes 

 so slight that it is impossible to say, from these alone, whether or no one is 

 dealing with distinct species ; the minute distinctions observed might be due 

 to the parasites being in different hosts, for it is known that the same form 

 often varies somewhat (e. g. in size), according to the host in which it is. 

 Laveran and Mesnil, however, have performed a series of instructive experi- 

 ments (see 52 and 53) tending to prove that an animal which has been 

 successively immunized against one Trypanosome and its disease is still liable 

 to, at any rate, certain others. Hence there is great probability that a try- 

 panosomosis of any particular region (when it is not, obviously, one which 

 has been transmitted thither from another locality) is produced by a distinct 

 species of parasite. This view is also supported by the specialised and 

 limited facilities for distribution which Trypanosomes possess. 



The pathogenic effects are nearly all referable to disorganisation either of 

 the circulatory, or of the nervous system, or of both combined. Fever 

 always occurs, at some time or other, during the course of the malady. Its 

 manifestation is extremely irregular, both in character and in time of 

 occurrence, and it is therefore usually readily distinguishable from malarial 

 fever. It may be variable or continuous ; in the former case it appears to 

 be generally remittent rather than intermittent, the temperature, although 

 varying considerably, remaining, for the most part, above the normal. 

 There are, however, often periods of apyrexia, and the temperature may 

 also fall below the normal, especially towards the close of the illness. 

 There is, particularly in chronic cases, marked and progressive anaemia and 

 emaciation, leading to pronounced enfeeblement, which is, in fact, the most 

 characteristic symptom of naturally occurring trypanosomosis. The loss of 

 red blood-corpuscles is frequently great (the number may diminish by as 

 much as 50 per cent.), and hsematuria is also met with, though never to the 

 same extent as in piroplasmosis. Another common feature is the occurrence 

 of oedematous swellings in various parts, chiefly in the neighbourhood of 

 the genitals, of the abdomen, and around the eyes. The parasites are often 

 more numerous in the bloody serosities bordering these places than in the 

 general circulation. This fact is of great importance in connection with the 

 transmission of Dourine. In this disease the parasites are extremely rare in 

 the blood, but are generally numerous in the immediate neighbourhood of 

 the oedematous excoriations on the penis, so that, in coitus, they come into 

 contact with the vaginal mucous membrane of a healthy mare, through 

 which they are able to pass. Among other externally visible symptoms 

 which are met with in certain instances and to varying degrees may be 

 mentioned the following: — "staring of the coat," or localised bristling of 

 the hair ; appearance of small naked areas of skin owing to the falling out 

 of the hairs ; occurrence of sanguineous subcutaneous clots, which usually 



