GASTROPHILUS HAEMOEEHOIDALIS AND OTHER BOTS. 35 



according to species, and placed under favorable rearing conditions. 

 It is evident that larva? within the stomach and duodenum are not 

 capable of withstanding the internal processes which accompany 

 the decomposition of animal tissues, especially during warm periods. 

 There is excessive gas formation with the breaking down of the tis- 

 sues, and the larva? apparently become asphyxiated, since they are 

 found bloated and when crushed become flat. During cool periods 

 larva? are affected very little for a number of hours, and in stated 

 cases as long as 30 and 48 hours after death of the host larva? have 

 been reared to adults. Low temperatures hold back that period of 

 decay in the carcass which normally would cause the death of larva?. 

 From post-mortem examinations, as will be seen in Table I, 

 G. haemorr holdalls larva? are seldom found in the rectum. In all 

 probability they drop shortly after death, and during the normal 

 period of dropping are capable of producing adults. 



CONTROL STUDIES. 



REMOVAL OF G. HAEMORRHOIDALIS LARV^ FROM RECTUM. 



The effectiveness of the extraction of Hypoderma larva? as advocated 

 by various authors suggests a mechanical removal of G. haemorr - 

 hoidalis larva?. While they appear at the margin of the anus daily, 

 studies show that they remain visibly attached from 40 to 71 hours. 

 This would necessitate much work during a busy season with farm- 

 ers, but extractions at feeding time would greatly reduce the number 

 in work animals. In practice this periodical detaching caused much 

 discomfort and soreness about the anus. 



The attachment of clusters of larva? within the rectum and the 

 recommendation of tobacco decoctions, by the Bureau of Animal 

 Industry (1911), for larva? lodged in the rectums of horses, indi- 

 cated the need of information as to the effect, on this species of 

 Gastrophilus, of substances used as enemas. This necessarily re- 

 quired a detailed study of the effects of various substances upon 

 larva?, and these are reported in Table VIII. 



