126 GENERAL CONCLUSIONS. 



Serpents take their loud in large quantities, often swallowing animals heavier 

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

 absorption into the blood, a large portion of which is superfluous, and must be 

 eliminated by the kidneys. The carnivorous Chelonians, on the other hand, are 

 much more moderate, and slow in the indulgence of their appetites. This arises 

 from necessity rather than choice. Their motions are so slow, their disposition to 

 shut themselves up in their shells so great, and their mouth so small, that their 

 appetites are not indulged to such an extent as to burden the kidneys, and call 

 for an increase in their size. 



The rapidity of the wastes of the tissues, as we have previously shown, is pro- 

 portional to the rapidity of the vital actions. Hence, the kidneys will have more 

 to do in active animals than in the sluggish. Many serpents, as the black snake 

 and coachwhip snake, are remarkably active, and all Ophidians are more energetic 

 than the proverbially sluggish Chelonians. Here we have another reason why the 

 kidneys should be larger in the former than in the latter. Those Chelonians which 

 inhabit the water should have smaller kidneys than those Ophidians which inhabit 

 the land, because the function of the skin is much more active in the former than 

 in the latter. The skin of most serpents is completely covered by horny scales, 

 and its power of removing fluids, and, the products of the metamorphoses of the 

 tissues must be very feeble. 



2. As far as my observations have extended, it may be asserted, as a general 

 rule, that the kidneys are relatively larger in the carnivorous than in the frugivorous 

 or granivorous birds. In the carnivorous birds, the intestinal canal is much shorter 

 than those living upon a vegetable or mixed diet. Their food is capable of more 

 rapid digestion, and introduction into the circulation, and as a necessary conse- 

 quence, the organ which regulates, in a great measure, the amount of the solid and 

 fluid materials of the blood, and eliminates all waste and useless matters, must be 

 correspondingly large. Carnivorous birds also appear to be more active and ener- 

 getic than the frugivorous or granivorous. 



Another reason is found in the chemical constitution of the food. This, however, 

 will be considered when we come to study the same law in the Mammalia. 



3. The kidneys of the carnivorous Mammalia are relatively larger than those 

 of the graminivorous or frugivorous ones. This may be stated to be generally 

 true, as far as our observations have extended. 



If the character of the food, the structure and size of the digestive apparatus, 

 and the habits of the two classes of animals, be attentively considered, we will 

 understand at once why this relative difference should exist in organs fulfilling the 

 same office in both. 



The food of the Carnivora, as the name implies, consists of flesh and blood, which 

 is capable of ready digestion and absorption, and rapidly supplies the wants of the 

 animal economy. The intestinal canal is in all cases short when compared with 

 that of the Mammalia, which feed on vegetable substances. Carnivorous animals 

 have voracious, and, in most cases, almost insatiable appetites. They gorge them- 

 selves with food, which is capable of entering the circulation with little or no 

 alteration, and rapidly supplies the wants of the economy. There must be 

 some organ to act as a safety-valve, and remove quickly the large unnecessary 



