VOL. XXI. 3 PHILOSOPHICAL TRANSACTIONS. 37g 



the fly and its powder, to try if he could perceive any sharp instruments in those 

 animals, but without discovering any such thing in the fly ; and the powder was 

 seen only as a dark cloud. He next put half a pound of cantharides into a 

 retort, with a small sand heat, and in a very short time there came over vast 

 quantities of animalcules, so very small, that he was not able to discern 

 their shape ; that very little salt adhered to the neck of the retort, and the 

 volatile salt shot into beautiful crystals in the receiver, and that of the 8 oz. of 

 cantharides only 2 oz. 5 dr. were left as a caput mortuum in the retort. When 

 the liquor came to be purified, the smallest heat suddenly brought over oil, salt, 

 and spirit, which could not be separated, but by repeated operations with brick- 

 dust. He mixed the spirit with salt of wormwood, spirit of hartshorn, and 

 sal-ammoniac, yet without fermenting ; but with spirit of vitriol it fermented 

 very strongly. 



In inquiring how wounding the skin by cantharides makes the pulse not so 

 quick, and consequently the blood to have a slower and more natural motion, 

 he considers that the heart being a muscle, and contracted at every pulse, is 

 not either the chief or sole cause that determines and stretches the sides of 

 the arteries, and so making a pulse, or a very extraordinary measure of such 

 distensions. These contractions having always been supposed to be performed 

 by an influx of spirits into the fibres of the muscles so contracted ; the ques- 

 tion now becomes, how wounding by cantharides makes the contraction of the 

 heart weaker ? After rejecting other methods as inadequate to this efi^ect, the 

 doctor concludes, that the only way by which a blister can produce its effect is 

 by wounding the channel that conveys those animal spirits which contract the 

 heart, give a quick pulse and a fever, with all its attendants, as deliriums, &c. 

 Thus then, the least quantity of animal spirits let out by the w^ounds of the 

 cantharides, will in a very little time proportionably weaken the heart's con- 

 traction, and give a slower pulse, which is all that is wanted. 



But how to apply a blister that may most effectually wound the conveying 

 nerves, we must recollect that the 8th pair of nerves, which serves for the 

 heart's contraction, has its rise from the sides of the medulla oblongata, behind 

 the processus annularis, by several threads which join together, and pass out 

 by the same hole that the sinus laterales discharge themselves into the jugulars; 

 and since the union by the atlas is not so firm and compact as in the other 

 vertebrae, there is no extraordinary hindrance why some of these wounding 

 particles may not reach that nerve, since either it, or considerable branches of 

 it, run superficially enough on the neck. 



Hence the doctor concludes : 1. That the operation of a blister is great,and 

 sudden. 2. That the wounding of this nerve, or a branch of it, is so neces- 



3c 2 



