130 OBSERVATIONS ON THE 



sition of its body without any excrementitious residue, though on dis- 

 section the intestine is found to contain a yellow or greenish matter, 

 which is derived from the color of the food, and shews that the chyle, 

 as the larva receives it, is not perfectly pure. 



The slowness of their growth and the purity of their food must 

 occasion what tliey receive in a given time to be proportionable small : 

 from whence probably arises the extreme difficulty of destroying them 

 by any medicine or poison thrown into the stomach. After opium had 

 been administered to a horse laboring under a case of locked jaw for a 

 week, in doses of one ounce every day, on the death of the animal, 

 bots have been found in the stomach perfectly alive. Tobacco has been 

 employed in much larger quantities in the same complaint, and has been 

 also longer continued without destroying them. They are also but 

 rarely affected by the drastic purgatives which bring away in abundance 

 other animal parasites. 



It is the opinion of experienced veterinary surgeons, that the bots 

 are not so injurious to horses as is generally conceived. When remov- 

 ed from the stomach, a deep impression remains where they adhered ; 

 but whether they ever irritate it so as to bring on a fatal spasm of the 

 stomach itself, or of the pylorus, or, by collecting round this passage, 

 prevent the food from entering the intestine, has never been investigated 

 with sufficient accuracy. The surprise of some farriers and farmers on 

 opening the stomach after death, and being presented with so singular 

 an appearance as the bots, has, without doubt, very often occasioned the 

 death to be attributed to these, though it is certain that but few horses 

 escape them. A few observations on the utility of such local irritations 

 were made in No. 1., and I will here add, that it is remarked by per- 

 sons of observation, that those horses which are not exposed to the 

 bots, are more frequently infected witli the glanders and other diseases, 

 than those which are exposed to the attacks of the bots. 



These grubs attain their full growth about the latter part of May, 

 and come from the horse per anum, from this time until the close of 

 June, or sometimes later. On dropping to the ground, they find out 

 some convenient retreat, and change to tlie chrysalis : and in about six 

 or seven weeks the fly appears. Fig. 3, male ; fig. 4, female. 



The mode pursued by the parent fly to obtain for its young a situa- 

 tion in the stomach of the horse, is truly singular, and is effected in the 

 following manner : — When the female has been impregnated, and the 

 eggs are sufficiently matured, she seeks among the horses a subject for 

 her purpose, and approaching him on the wing, she holds her body 

 nearly upright in the air, and her tail, which is lengthened for the pur- 



