CALORIFICATION. 95 



activity at the time when the evolution of heat is most remarkable — 

 that of germination and flowering. 



In animals an exact conformity may be perceived between the 

 amount of oxygen consumed and of carbonic acid given off, and the 

 amount of heat liberated. Some physiologists have thought that 

 this carbonic acid was formed in the lungs, and the .resulting 

 heat distributed to the system by the arterial vessels, they having a 

 greater capacity for heat than the veins ; but it has already been 

 shown that the carbonic acid is formed in the tissues and not in the 

 lungs ; as the latter, therefore, cannot be the point at which the heat 

 is generated, it must be evolved throughout the system. Exercise, 

 or any increase in the nutritive operations of a part, is always 

 attended with an elevation of temperature, as well as an increase in 

 the extrication of carbonic acid. 



The formation of carbonic acid by the union of the oxygen 

 absorbed from the air with the carbon set free from the body, is the 

 main source of the heat generated within the animal system. The 

 amount of carbon consumed in 24 hours is not sufficient, however, 

 to account for all the heat liberated ; we must therefore look to other 

 sources. That it is not de'pendent on nervous influence is evident 

 from the fact that the process occurs in vegetables. Perhaps the 

 formation of the various secretions, — fluids having a less capacity 

 for heat than arterial blood, — may be accompanied with the elimina- 

 tion of some latent heat. It is also suggested that the union of 

 oxygen with hydrogen, phosphorus and sulphur, and the conversion 

 of the plastic fluids into solids may likewise explain the source of 

 some of the heat that is unaccounted for. 



That the cutaneous respiration is subservient to the maintenance 

 of the heat is evident from the fact that if the hair of rabbits be 

 shaved off*, and the surface covered with varnish, the temperature 

 instant! y/a//5. 



Diseases that involve an accelerated pulse and augmented respira- 

 tion are generally accompanied with elevation of the temperature. 

 The converse is also true. The ordinary temperature of the human 

 body ranges from 98° to 100° Fahr., varying but a few degrees 

 above or below when the temperature of the surrounding medium is 

 elevated or depressed. 



Man is able to resist high degrees of temperature, (provided the 

 surrounding air be dry,) by the evaporation of the perspiratory 

 secretion from the surface of his body. The less the age of the 

 individual, the less is his ability to maintain an independent tempera- 

 ture ; the human infant in this respect resembles a cold-blooded 

 animal. 



EEPRODUCTION. 



See Obstetrics, in which this function is treated of. 



