GENERAL VIEW OF THE ANIMAL FUNCTIONS. 99 



gans, it comes into very near proximity with the blood in the capil- 

 laries of that part of the circulation named, as before mentioned, the 

 pulmonary circulation ; and there an important interchange of certain 

 gases takes place, through the coats of the pulmonary capillaries, 

 between the blood and the inspired air. The air receives, besides 

 moisture, a certain quantity of carbonic acid, an excreted product 

 from the impure or venous blood. Thus the lungs become important 

 excretory organs, so important that the arrest of respiration is speedily 

 followed by death. But more than this, the inspired air imparts to 

 the blood a like quantity of oxygen, which converts the venous or im- 

 pure blood, brought from the body through the systemic circulation 

 to the heart and thence propelled through the pulmonary circulation 

 to the lungs, into pure or arterial blood, which goes back to the heart, 

 and is thence again propelled into the systemic vessels of the whole 

 body. The air taken into the lungs is therefore the source of the 

 oxygen of the arterial blood, which nourishes the whole frame, and 

 especially stimulates the muscular and nervous tissues, and so main- 

 tains the proper animal functions. This oxygen, moreover, is the 

 main agent, as it would seem, in the disintegration of those two tis- 

 sues ; and the chemical changes effected by its union with their mole- 

 cules, are intimately associated with the exercise of their special prop- 

 erties of contractility and excitability so much so, that these proper- 

 ties cannot be manifested without chemical change or oxidation. The 

 chemical work thus performed is probably, as we shall see, truly cor- 

 related with the motor or mechanical work, i. e., with the contractile 

 power of the muscles, and also with the more recondite nervous action; 

 partly, also, it is transformed into animal electricity in these two tis- 

 sues ; and lastly, the oxygen of the air, in producing these chemical 

 changes within the body, all more or less stages of oxidation, likewise 

 produces, as in cases of ordinary combustion, an elevation of temper- 

 ature in the animal frame. Respiration is therefore the functional 

 source of animal heat, an important use of this function in the econ- 

 omy, being to produce such heat. In the warm-blooded animals, 

 however, the oxidation of the tissues only, is insufficient to produce 

 an amount of heat adequate to maintain the other functions of their 

 economy, whether animal or vegetative ; and hence, such animals take 

 in their food certain additional materials, besides those used for the 

 nutrition of the tissues materials which merely enter the blood, and 

 therein become oxidated or burnt, for the purpose of producing the 

 required additional amount of heat. Unless, therefore, the animal 

 here supposed to be under observation, be supplied with fat as well as 

 flesh, its activity is lessened, its health is impaired, and its body seri- 

 ously emaciated. 



The entire series of vegetative functions, which we have now ex- 

 amined, viz., digestion, absorption, circulation, nutrition, sanguifica- 

 tion, secretion, excretion, and respiration, are named, as we have seen, 

 the nutritive vegetative functions, because they are concerned espe- 

 cially in the maintenance and support of the body of the individual 

 animal. They supply the large and constant wants of the proper 

 animal organs of motion and sensation, but their healthy performance 



