DEVELOPMENT OF HEAT. 685 



seasonal degree ; the heat lost by Sparrows in August being much less than that lost by 

 birds of the same species in July. 



895. Our knowledge of the dependence of all the vital processes in warm- 

 blooded animals, upon the Heat of their bodies, and of the dependence of 

 their Calorifying power upon the due supply of material for the Chemical 

 changes which generate Heat, has lately received some very remarkable 

 additions from the experiments of M. Chossat.* He found that Birds, when 

 totally deprived of food and drink, suffered a progressive, though slight, daily 

 diminution of temperature. This diminution was not so much shown by a 

 fall of their maximum heat, as by an increase in the diurnal variation, which 

 he ascertained to occur even in the normal state. The amount of this varia- 

 tion, in Birds properly supplied with food, is about l Fahr. daily; the 

 maximum being about noon, and the minimum at midnight. In the in- 

 anitiated state, however, the average variation was about 6, gradually 

 increasing as the animal became weaker: moreover, the gradual rise of tem- 

 perature, which should have taken place between midnight and noon, was 

 retarded; whilst the fall subsequently to noon commenced much earlier than 

 in the healthy state; so that the average of the whole day was lowered by 

 about 4^ between the first and tine penultimate days of this condition. On 

 the last day, the production of Heat diminished very rapidly, and the ther- 

 mometer fell from hour to hour, until death supervened; the whole loss on 

 that day being about 25 Fahr., making the total depression about 29. 

 This depression appears, from the considerations to be presently stated, to be 

 the immediate cause of Death. On examining the amount of loss sustained 

 by the different organs of the body, it was found that 93 per cent, of the Fat 

 had disappeared, all, in fact, which could be removed; whilst the Nervous 

 Centres scarcely exhibited any diminution in weight. The loss of weight of 

 the whole body averaged about 40 per cent.; and that of the various other 

 component tissues was very much what might have been anticipated. From 

 the constant coincidence between the entire consumption of the Fat, and the 

 depression of Temperature, joined to the fact that the duration of life under 

 the inanitiating process evidently varied (other things being equal) with the 

 amount of Fat previously accumulated in the body, the inference seems 

 irresistible, that the Calorifying power depended chiefly, if not entirely, on 

 the materials supplied by this substance. The maintenance of the normal 

 amount of matter in the Nervous centres, is a very remarkable fact; and 

 seems to countenance the idea, that the substances peculiar to Nervous tissue 

 may be formed from Fatty matter, rather than from a Proteine-compound 

 ( 249). 



896. Whenever, therefore, the store of combustible matter in the system was 

 exhausted, whether by the Respiratory process alone, or by this in conjunc- 

 tion with the conversion of Adipose matter into the materials for the Nervous 

 or other tissues, the inanitiated animals died, by the cooling of their bodies 

 consequent upon the loss of Calorifying power. That this is the real expla- 

 nation of the fact, is shown by the results of a series of very remarkable ex- 

 periments performed by M. Chossat, with a view of testing the correctness 

 of this view. When inanitiated animals whose death seemed impending (in 

 several instances death actually took place, whilst the preliminary processes 

 of weighing, the application of the thermometer, &c., were being performed), 

 were subjected to artificial heat, they were almost uniformly restored from a 

 state of insensibility and want of muscular power to a condition of compara- 

 tive activity; their temperature rose, their muscular power returned, they flew 



* Recherches Experimentales sur 1'Inanition, Paris, 1843. See, also, the Brit, and For. 

 Med. Rev. for April, 1844. 



58 



