116 M. Flourens on the effects of 



want of excitation, act in nearly the same manner, the first by 

 diminishing the external heat, and the second, by preventing 

 the internal heat from developing itself. 



It has been said that light and the presence of food are hos- 

 tile to lethargy, but, according to my experiments on the lerot, 

 these causes have little or no influence. 



I now come to the internal or organic conditions ; and it is 

 important to determine^r^^, on what organ, or particular or- 

 ganic modification, lethargy depends ; and secondly, what is the 

 mechanism of this phenomenon. 



On both these points, however, we possess only conjectures, 

 and, with respect to the first, there is scarcely an organ to 

 which these conjectures have not been successively applied. 



The two organs which have been particularly selected, are 

 the encephalon and the thymus-^ — the encephalon^ to which 

 physiologists have long been in the habit of referring what 

 they could not otherwise explain ; and the thymus, a glan- 

 dular body, situated in the front of the neck, and penetrating 

 to the heart, and to which the mode of its developement gives 

 a particular claim to perform the principal part in lethargy. 



This organ, indeed, is in the highest degree of enlargement 

 at the moment when the animal falls asleep. It collapses at 

 the time when it awakes, and amongst the mammalia it dis- 

 appears almost entirely at the adult age, and is only developed 

 in the foetus, the state of which, in the womb of the mother, 

 approximates it by so many points to the state of the torpid 

 animal. 



These two conjectures will deserve to be submitted to ex- 

 periment, particularly in the present day, when the experimen- 

 tal method has localized so many other phenomena, and when, 

 to speak only of my own experiments on the encephalon, it 

 has succeeded in determining a distinct organ for the sensations, 

 an organ for the movements of locomotion, an organ for the 

 motions of reproduction, and has even found a point to which 

 it is sufficient for any part to be attached to live, and from 

 which it is sufficient that it be detached to die, and which thus 

 constitutes the central and vital part of the animal economy. 

 I therefore suppressed, in succession, the different parts of 

 the encephalon in different lerots. The suppression of some 



