74 Mr. W. Sells' Observations 



dipping into the muscular tissue, with raised callous edges, con- 

 taining a kind of lardaceous matter ; at most of the points where 

 the insect has imbedded its head and part of its body, a circular 

 warty enlargement appears, and upon squeezing the surrounding 

 hardened portion where a larva is deeply lodged, some of the 

 thick white substance alluded to was forced out, but without 

 compelling the bot to quit its hold: on the other hand, the cuti- 

 cular portion which had been attacked exhibits but slight com- 

 parative injury. The preceding observations, in connexion with 

 the physiological views which could hardly fail to present them- 

 selves, have led me to a conclusion quite at variance with the 

 opinions of Mr. B. Clark as to the mode in which the bot is 

 nourished, but which it may not unfairly be presumed has been 

 long since modified by that gentleman's further consideration and 

 enlarged experience. 



The horse's stomach is a large macerating bag for the vast 

 quantities of vegetable food of which it is the recipient, and where 

 its digestion is but partially accomplished, that process being com- 

 pleted in the expanded head of the colon. Now Mr. Clark's idea 

 of the bots feeding either upon the gross vegetable substances, or 

 the watery juices obtained from them in union with the secretions 

 of the stomach, (and which, when in a state to be allowed to pass 

 out of it by the pylorus, is called chyme,) is, to my mind, entirely- 

 erroneous. The bot, when once fixed by the peculiar cross-locking 

 of its tentacles, rarely quits its hold until full grown and ready to 

 pass into pupa, and no doubt is mainly supported by sucking 

 fluids from the vascular structure of the horse's stomach, and im- 

 bibing matters secreted in consequence of the wound it inflicts 

 upon the coats of that organ, and where, as a foreign body, it 

 proves a constant irritant ; this will account for the common 

 failure of attempts made for the removal of bots by the adminis- 

 tration of large doses of opium, tobacco, aloes, calomel, or castor 

 oil, as these several substances do not in that case become mixed 

 with the proper food of tlie insect. 



As regards the probable effects of the Gasterophili upon the 

 health of the animals which they inhabit, the opinion which I 

 shall venture to advance on this matter will tend to prove that I 

 have not been able to take quite so favourable a view of the inno- 

 cence, and, indeed, positive salubrity, of these inmates of the 

 digestive apparatus of the horse, as we find in Mr. Clark's Essay ; 

 where, in addition to many sensible and scientific remarks, the 

 author gives some interesting illustrations of the importance of 

 counter-irritants, as the happily provided means of preventing 



