136 COMPARISON OF COLD AND WARM-BLOODED ANIMALS. 



The results of these experiments demonstrate conclusively that, as the solids and 

 fluids of the animal economy are developed, the temperature elevated, and intellect 

 perfected, the compositions, decompositions, and metamorphoses of the organic and 

 inorganic elements become more rapid and abundant. 



When we compare the relative size of the kidneys, and the amounts of their 

 excretions in different animals, the question immediately arises : Why should cold- 

 blooded animals, whose circulation is sluggish, which eat but seldom, often abstain- 

 ing from food for months, whose habits are indolent, and whose excretions and 

 secretions are exceedingly small, be provided with large urinary organs ? 



In warm-blooded animals it is natural to suppose that an elevated temperature, 

 rapid circulation, and active energetic mode of life, should call for large organs 

 capable of removing in an efficient manner from the blood the products of the dis- 

 integrations of the system ; but why should we have in a condition of things directly 

 contrary, in every respect, as large organs, to perform the same office in a much 

 feebler degree. 



In attempting to explain this phenomenon we must consider the following facts 

 and laws of the animal economy : — 



The blood contains a definite amount of materials to be eliminated by the kidneys, 

 diffused throughout its entire mass. That all these materials should be separated, 

 the entire mass of the blood must be presented to the kidneys, and the rapidity of 

 the elimination will depend upon the rapidity of the circulation, and the activity 

 of the excreting cells and the size of the organs. 



Temperature also exerts a great influence upon all the actions of the animal 

 economy. 



If the temperature of cold or warm-blooded animals be reduced much below the 

 normal standard their functions will gradually become more feeble, and finally 

 cease. 



It may be stated, as a general law, that the lower the temperature of any organ 

 the more feeble will be its action. 



Nervous force exerts a great influence upon the circulation, and, through it, upon 

 secretion and excretion. 



It is known to every naturalist that cold-blooded animals have much less mus- 

 cular and nervous power in proportion to their size than the warm-blooded ones. 



From these considerations, then, it is evident that to perform the same office, to 

 excrete precisely the same amount, larger organs are required in the cold than in 

 the warm-blooded animals. 



In Ophidians which have relatively larger kidneys than the other cold-blooded 

 animals, in addition to the reasons stated above, the character of their alimentary 

 canal and their habits render the existence of large kidneys necessary. 



These animals are carnivorous and have a short alimentary canal, which, in many 

 instances, is almost completely straight. 



They take their food in large quantities, often swallowing animals heavier and 

 larger than themselves. All this animal matter is capable of digestion and absorp- 

 tion into the blood, a large portion of which is superfluous. 



The great channel for the elimination of this is through the kidneys; the lungs 

 being mere sacks, and performing the function of respiration in an imperfect manner. 



