422 OF SECRETION. 



liability to inflammation and ulceration of the walls of the alimentary 

 canal, and of their contained glandulse. 



5. General Summary of the Excreting Processes. 



751. We have now passed in review the various processes, by which 

 the products of the disintegration of the animal tissues are carried 

 off; and we have seen that the necessity for their removal is much 

 more urgent than for their replacement. A cold-blooded animal may 

 subsist for some weeks, or even months, without a fresh supply of food, 

 the waste of its tissues being so small, if it remain in a state of rest, as 

 to be quite compatible with the continuance of its life ; and a warm- 

 blooded animal may live for many days or even weeks, provided that it 

 has in its body a store of fat sufficient to keep up its heat by the com- 

 bustive process. But in either case, if the exhalation of carbonic acid 

 by the lungs, the elimination of biliary matter by the liver, the separa- 

 tion of urea or uric acid by the kidneys, or the withdrawal of putrescent 

 matter by the intestinal glandulae, be completely checked, a fatal result 

 speedily ensues ; more speedily in warm-blooded animals, than in those 

 which cannot sustain a high independent temperature, on account of 

 the greater proneness to decomposition in the bodies of the former, than 

 in those of the latter ; and more speedily in the latter, when their 

 bodies are kept at an elevated temperature by the warmth of the sur- 

 rounding medium, than when the degree of heat is so low, that there is 

 little proneness to spontaneous change in the substance of their bodies. 



752. It may be taken as a general principle, in regard to the Ex- 

 creting processes (including Kespiration), that they have a threefold 

 purpose ; in the first place, to carry off the normal results of the waste 

 or disintegration of the solid tissues, and of the decomposition of the 

 fluids ; in the second place, to draw off the superfluous alimentary 

 matter, which though received into the circulating current, is not con- 

 verted into solid tissue, in consequence of the want of demand for it ; . 

 and in the third place, to carry off the abnormal products, which 

 occasionally result from irregular or morbid changes in the system. 

 Thus by the Lungs are excreted a large amount of carbon, and some 

 hydrogen, resulting from the disintegration of the tissues, especially 

 the nervous and muscular ; the same elements, in animals that take in a 

 large proportion of farinaceous or oleaginous aliment, may be derived im* 

 mediately from the food, withput any previous conversion into solid tissue ; 

 and there can be little doubt that the respiratory function is also an impor- 

 tant means of purifying the blood from various deleterious matters, 

 either introduced from without (such as narcotic poisons), or generated 

 within the body (such as the poison of fever).* And it is important 

 to bear this last circumstance in mind ; since it enables us to understand 

 how, if time be given, the system frees itself from such noxious sub- 

 stances ; and points out the duty of the medical attendant to be rather that 



* There is strong reason to believe that, in many instances, a small amount of poi- 

 sonous matter introduced from without, in the form of a contagion or miasm, may lead, 

 by a process resembling fermentation, to the production of a large quantity of similar 

 noxious substances in the animal fluids. 



