NUTRITIO.V. 155 



ed in inquiries of this kind, and every intelligent man should feel such 

 an interest. 



The source of the various secretions is the great circulating fluid, 

 the blood. This is not only the universal nourisher of the various tis- 

 sues of the body, but likewise the contributor of materials for the dif- 

 ferent laboratories of the animal system, in which chemical results are 

 produced b} chemical laws under the control of vital agencies. Its con- 

 stituents, it does not appear necesrjary to our purpose, which involves 

 merely a general representation, to present; suffice it to say, it contains 

 every thing necessary to subserve animal necessities. Heat is necessary 

 to animal life, and it has been generally admitted since the rise of pneu- 

 matic chemistry, that something similar to combustion is carried on in 

 the lungs, or in the system. The earlier theories were simple ; they 

 represented the matter as merely a combination of the oxygen of the 

 atmosphere with the carbon of the venous blood, and the consequent 

 disengagement of heat. 



This simple view was not considered tenable, and it was supposed 

 to be ascertained by crucial experiments that the nervous system exer- 

 cised much control over the production of animal heat. It would re- 

 quire much time to unfold the various modifications of the* primitive 

 theory, but they are all more or less allied to combustion in their ele- 

 ments. Nor has Liebig presented a system fundamentally different. He 

 transfers combustion from the lungs to the capillary system. This is 

 said to be "the fire chamber where the fuel is consumed, which is des- 

 tined to set in motion the whole machinery of life." ''Internal capill- 

 ary combustion is the source of animal heat." 



"Carbon and hydrogen are burned in the blood, as remarked by 

 Fownes, and this to an extent which will strike with surprise, and at 

 first, incredulity, those unaccustomed to sucli considerations. Many 

 ounces of carbon are, in every individual, daily rejected from the lungs 

 as carbonic acid. It is impossible that combustible matter can thus be 

 disposed of without the evolution of a vast amount of heat, as much 

 heat, in fact, as if it had been burned in a fire-grate. This heat is man- 

 ifest in the elevation of the temperature which the animal frame always 

 possesses above that of the surrounding medium, an elevation of tem- 

 perature always in direct proportion to the amount of nervous and mus- 

 cular energy of the animal, and to the vigor of its respiration, but never 

 in any single case altogether absent." The lungs and the skin throw 

 ofT carbonic acid, the product of combustion. Some of the secretions 

 may be considered as defecatory or purifying, and animal fat is a de- 



