200 Mr. Clark s Obfervatlons eh the Genus Oeftrus, 



The flownefs of their growth and the purity of their food ftitift 

 occafion what they receive in a given time to be proportionately 

 final! ; from whence probably arifes the extreme difficulty there is 

 found in deftroying them by any medicine or poifoii thrown into 

 the ftomach. After opium had been adminiftered to a horfe labour- 

 ing under a cafe of locked jaw for a week, in doles of one ounce 

 every day, on the death of the animal I have found the bots in the 

 ftomach perfectly alive. Tobacco has been employed in much 

 larger quantities in the fame complaint, and has been alfo longer 

 continued without deftroying them. They are alfo but rarely af- 

 fected by the draftic purgatives which bring away in abundance the 

 'Tenia? and Afcaridcs. 



I do not apprehend they are {o very injurious to the horfes as is 



generally conceived. When removed from the ftomach a deep im- 



preflion remains where they adhered ; but whether they ever irritate 



it fo as to bring on a fatal fpafm of the ftomach itfelf, or of the 



pyioruSy or, by collecting round this paffage, prevent the food from 



entering the inteftine, has, I believe, never been investigated with 



furfkient accuracy. The ignorant furprife of farriers on opening 



the flomach after death, and being prefented with fo fingular an 



appearance as the bots, has, without doubt, very often occafioned the 



death to be attributed to thefe, though it is certain but few horfes on 



our commons can efcape them. At the extremity of the truncated 



end are feen two protuberant kind of lips, applied to each other. See 



fig. 7, a. When thefe unfold, or are removed with the knife,, a plate 



of horny or cartilaginous confidence is feen, having fix femicircular 



lines, with their points oppofed to each other. See fig. 23. Thefe 



lines are rough, and made up of alternate deprefled and elevated 



fpots of black and white. 



Through this plate the air is admitted to fill the air tubes; and in 



moil 



