the action of Cold on Animals. 117 



of them prevented the animal from falling under lethargy, 

 and the suppression of others appeared even to hasten it. 



The result was similar for the thymus, and its suppression 

 rather accelerated than retarded the action of lethargy. I 

 have, besides, constantly observed, that whatever debilitates 

 the animal has the same effects upon it as these suppressions. 

 Among my lerots the youngest and weakest always require a 

 less degree of cold than adults in order to become torpid. 



These experiments show that it is neither in the encephalon 

 nor in the thymus, that the principle which determines lethar- 

 gy resides. Those which follow seem to show what is the me- 

 chanism of this phenomenon. 



The carotids having been laid bare in a lethargic lerot^ 

 by an operation which might be supposed to be painful, but 

 which the animal scarcely feels, I found that they did not beat 

 even after the operation more than nine or ten pulsations in a 

 minute. Some time afterwards, striving more and more to 

 awake, and the respiration renewing itself, they beat 20, then 

 30, then 45, then 100, and lastly 110 pulsations in a minute, 

 when the respiration was perfectly re-established. 



The lei^ot being then exposed to the action of cold, I ob- 

 served its respiration grow weaker and weaker by degrees, and 

 its carotids at first beat 100, then ^5^ then 50, then 30, then 

 20, and finally 8 or 9 pulsations per minute, when the pulsa- 

 tions were again quite extinguished, and the animal quite le- 

 thargic. 



It was now interesting to determine if the artificial suspen- 

 sion of respiration would not bring about the same results as 

 that which had brought about lethargy. 



The respiration was now artificially suspended in a lerot 

 awake ; the blood of the carotids soon became black, and the 

 number of pulsations more and more reduced. At the fourth 

 minute there were only thirty-two ; half an hour later there 

 were no more. The heart alone beat 8 or 9 pulsations, which 

 was precisely the number which I had found it to beat in the 

 preceding lerot in perfect lethargy. By suspending the re- 

 spiration in this experiment, I had reproduced the state of cir- 

 culation in lethargy, or more exactly, I had reproduced the le- 



