506 , NUTRITION. 



Products of Disassimilation. 



Excrementitious Principles. 



f Principally by the 



lungs; but also 



Carbonic acid ] by the skin, and 



in solution in the 

 (^ excreted fluids. 



Alkaline sudorates Perspiration. 



f Principally in the 



urine ; but a cer- 

 Urea j tain quantity in 



the perspiration. 



Urate of soda Urine - 



Urate of ammonia 



Urate of potassa 



Urate of lime 



Urate of magnesia 



Hippurate of soda 



Hippurate of potassa 



Hippurate of lime " 



Creatine " 



Creatinine 



Oxalate of lime " 



Xanthine " 



Stercorine (changed from cholesterine) Faeces. 



Excretine " 



In the above list we have omitted all doubtful excrementitious principles, as well 

 as the inorganic compounds found in the excreted fluids; and we may assume that 

 the substances therein enumerated represent, as far as we are now able to determine, 

 the physiological wear of the organism. We shall not again discuss the fact that the life 

 of tissues involves physiological waste or decay, and that the excrementitious principles 

 proper represent the final changes of organic substances. "We know that this process 

 goes on without necessarily involving exercise of the peculiar functions of the parts ; but 

 it is no less true that exercise, or work, increases the activity both of nutrition and wear. 

 This is one of the great principles underlying all our ideas of the process of nutrition. 

 "We shall not discuss here the influence of work upon the elimination of some of the 

 nitrogenized compounds, particularly urea, for we have already examined that subject 

 most carefully in another place ; but we have no hesitation in stating, as a general law 

 that has yet to meet with exceptions, that physiological work increases excretion. 



Animal Heat. 



The process of nutrition in animals is always attended with the development of heat, 

 and it produces a temperature more or less independent of external conditions. This is 

 true in the lowest as well as the highest animal organizations ; and analogous phenomena 

 have even been observed in plants. In cold-blooded animals, nutrition may be suspended 

 by a diminished external temperature, and certain of the functions become temporarily 

 arrested, to be resumed when the animal is exposed to a greater heat. This is true, to 

 some extent, in certain warm-blooded animals that periodically pass into a condition of 

 stupor, called hibernation ; but in man, and in nearly all the warm-blooded animals, the 

 general temperature of the body can undergo but slight variations. The animal heat is 

 essentially the same in the intense cold of the frigid zones and under the burning sun of 

 the tropics ; and if. from any cause, the body become incapable of keeping up its temper- 



