DEVELOPMENT OF HEAT. 579 



to 102, the temperature of the air being only 34^ at the time ! In all these 

 instances, the amount of Oxygen consumed bears an exact proportion to that 

 of the Heat evolved. Even in higher animals, exercise has a considerable 

 effect in producing an elevation of temperature ; and, that this is not merely 

 due to the acceleration of the circulation, is shown by the very curious fact, 

 that the exercise of a particular muscle will cause an increase in the heat 

 liberated from it, as shown by needles plunged in its substance, and connected 

 with the Thermo-Multiplier.* It may, indeed, be stated as a general propo- 

 sition, applicable as well to different parts of the same being, as to different 

 individuals, that the development of Heat is proportional to the activity of the 

 molecular processes which constitute the functions of Nutrition, Secretion, 

 &c. ; increasing with their activity, and diminishing with their torpor. It is 

 very easy to explain, on this principle, the known influence of the Nervous 

 system on the calorific function: since, although the molecular changes in the 

 organized fabric are not dependent upon the agency of that system, they are 

 very much influenced by it ; and thus we can readily understand how a state 

 of nervous excitement may produce an elevation of temperature, and a depres- 

 sion of nervous power occasion a cooling of the body. The experiments of 

 Sir B. Brodie, Chossat and others,- in which a greater or less portion of the 

 nervous centres was removed, and the animal cooled notwithstanding the 

 maintenance of the circulation, by no means prove that the Nervous system 

 is directly concerned in the production of heat ; since in all such experiments 

 there is a gradual loss of those other vital powers which are concerned in the 

 function of calorification. From the experiments of Dr. W. Philip and Dr. 

 Hastings, it appears that an animal whose nervous centres have been re- 

 moved, cools much faster when left to itself than when Artificial Respiration 

 is practised ; and that, if the cooling have made much progress before the 

 artificial respiration is caused to commence, the temperature may be raised ; 

 and this, too, in spite of the very imperfect manner in which natural Respi- 

 ration is replaced by movements artificially effected. 



726. That the maintenance of Animal Heat is due in part to those mole- 

 cular changes, to which the extrication of Carbonic acid through the Skin is 

 subservient, appears from the following experiments recently performed by 

 MM. Becquerel and Breschet. The hair of Rabbits was shaved off, and a 

 composition of glue, suet and resin, forming a coating through which air 

 could not pass, was applied over the whole surface. It might seem natural 

 to suppose that, by preventing the evaporation of the sweat, the temperature 

 of the tissues would be very sensibly increased ; and that, by this increase of 

 the temperature of the whole, body, a high state of fever would be engendered, 

 with the symptoms of which the animal would at last die. But the contrary 

 occurred. In the first Rabbit, which had a temperature of 100 before being 

 shaved and plastered, it had fallen to 89^ by the time the material spread 

 over him was dry. An hour after, the thermometer, placed in the same parts, 

 (the muscles of the thigh and chest) had descended to 76. In another Rab- 

 bit, prepared with more care, by the time that the plaster was dry, the tem- 

 perature of the body was not more than 65 above that of the surrounding 

 medium, which was at that time 625; and an hour after this the animal 

 died. These experiments place in a very striking point of view the import- 

 ance of the Cutaneous surface as a respiratory organ, even in the higher ani- 

 mals : and they enable us to understand how, when the secreting power of 

 the Lungs is nearly destroyed by disease, the heat of the body is kept up to 

 its natural standard by the action of the Skin. A valuable therapeutic indi- 



* See the experiments of MM. Becquerel and Breschet, in Ann. des Sci. Nat., N. S. 

 Zool., torn. vi. 



