97 THE AMERICAN NATURALIST [VOL. XL VII 



Superiority to environment, and not adaptation to it, is 

 secured through the irritability of the organism con- 

 sidered as a whole. 



The great mechanisms of the body which have this 

 function are several. First, the heat-regulating mechan- 

 ism, for by means of this organisms are rendered inde- 

 pendent of the temperature of their environments. They 

 can exist in the tropics or in the arctics and withstand the 

 extremes of our own climate, while maintaining their 

 activities. This is a complex mechanism consisting of 

 insulating material in the skin; trophic nerves to the 

 internal organs; a closed vascular system; a power of 

 rapid oxidation ; supra-renal capsules ; pancreas ; nervous 

 coordination; sweat glands; evaporation of water in the 

 lungs; temperature nerves. More than any other this 

 mechanism enabled the mammals to conquer the reptiles 

 and supplant them. The mammals became independent 

 of the temperature of their environments. A mechanism 

 not coming by jumps, but the rudiments found far down 

 in the fishes and slowly evolved. 



A second fundamental mechanism of great importance 

 for the mammals in supplanting the reptiles and other 

 animals probably was that concerned in immunity. Most 

 of the toxins of poisonous reptiles are of a protein nature. 

 The mammals have developed a mechanism, the details 

 of which are still obscure, but which apparently consists 

 in the conversion of these protein toxins into bodies which 

 neutralize the toxins from which they are formed, that is, 

 into antitoxins. We find, as a matter of fact, that at least 

 many of the mammals are able apparently to make an 

 anti-toxin out of any kind of a foreign protein. Besides 

 this mechanism of defense, useful against bacteria, as 

 well as against snakes, there is the primitive mode of 

 phagocytosis and the chemical method of defense, which 

 consists either in the prevention of absorption, or in the 

 chemical neutralization of the poison by union with other 

 substances. Thus the toxicity of phenols, benzoic acid 

 and many alkaloids are neutralized. By this mechanism 



