78 
Surra 
Out of 16 cases treated on the first system seven had a relapse, nine 
were cured. 
Sixteen ponies were treated on the second system, four had a relapse, 
12 were cured. 
Conclusions and Remarks. 
(1) Exception may be taken to the practice of regarding as cured 
cases which have been under observation without relapse for a period of 
three to six months only. The fact that, among the animals treated, 
there has not been one case of relapse occurring after a period of six 
weeks from the cessation of treatment, and that the majority of cases 
quoted as cured have been under observation for three to 14 months, 
establishes reasonable grounds for including all these animals under the 
head of “recoveries.” 
(2) Arsenious acid is, undoubtedly, a specific for surra in horses. It 
must be administered in full sub-toxic doses and at intervals; and not 
in continuous daily dosage. 
In the light of these results it is clear that, in the early experiments 
conducted by Lingard, Bruce and others, arsenic was given in too small 
an amount and in continuous treatment. 
Animals cannot tolerate the requisite amount of arsenic if the dose 
be too frequently repeated. There is also the objection that by continu¬ 
ous small doses, not only does the animal body, but also the trypanosomes, 
acquire a certain amount of tolerance to arsenic. 
(3) It is doubtful whether any advantage is gained by combining 
atoxyl with arsenious acid in the treatment of surra. The results of 
treatment with arsenious acid alone, given in 10 doses at an interval of 
one day, were superior to those where the arsenious acid was alternated 
with atoxyl. A single dose of arsenious acid alone keeps the blood 
free from trypanosomes for a period of 10 to 30 days and in some 
cases longer. When the same dose of arsenious acid is followed, 24 
hours after, by an injection of a full amount of atoxyl, this period is not 
increased. 
(4) Much has been written ou the therapeutic action of atoxyl. It 
was at first supposed that atoxyl owed its trypanocidal properties to the 
fact that it contains a large proportion of arsenic and that it was simply 
a means of administering a large amount of that drug without producing 
toxic effect. 
Levaditi and Yamanouchi (1908) consider that the curative power 
of atoxyl is due to its reduction and the formation of trypanotoxyl. 
