234 ^^ ^^^ Vital Principle, 



from fome fource from which it is detached by 

 the excifion of the part. 



3. Irritation of the medulla oblongata, or of 

 the nerves fupplying particular mufcles, occa- 

 fions ftronger contradlions than irritation of the 

 mufcles themfelves*. The fame author to whom 

 I owe this obfervation, furnifhes an experiment, 

 direftly proving that the aftion of feparated muf- 

 cles depends upon the nervous energy. " Five 



* minutes after taking out the heart of a frog, 

 ' I injected a folution of opium into its ftomach 



* and guts. In lefs than half an hour it feemed 

 « to be quite dead j for neither pricking nor 



* tearing its mufcles produced any contraftion 

 ' in them, or any motion in the members to 

 ' which they belonged. After cutting off its 

 ' head, a probe pufhed into the fpinal marrow 



* made its fore-legs contradl feebly f." Here, 

 n an animal fo tenacious of life, as commonly 

 o hop about vigoroufly long after the heart is 

 aken out, or the head cut off, the irritability 



of the mufcles, or, in other words, the living 

 principle, is deftroyed by the application of 

 opium to the ftomach and inteftines. Now, 

 circulation being previoufly flopped, by taking 

 out the heart, the opium could only a£l on the 

 nervous fyftem, which was ftill entire, and the 

 nervous power being deftroyed by the opium. 



• Whytt Vit. and Inv. Mot. p. 10. 



f Obf. on Irrit, and Senf. Exp. II. p, 310. 



the 



