Fitness in the Living World 325 



they may be rendered immune to the poison even when given 

 in lethal quantities. The venom of every poisonous snake 

 is highly specific, and the antidote for one kind of venom 

 will hot serve as an antidote for another kind. Furthermore, 

 it is certain that the ancestors of the guinea-pig, which is a 

 native of South America, could never have had any experi- 

 ence with the venom of the cobra, a native of India; and 

 yet the guinea-pig can form an anti-body against cobra 

 venom, and for every particular kind of venom its own 

 peculiar anti-body. One who has had diphtheria has ac- 

 quired a toleration for the diphtheria toxin, so that he is 

 thereafter usually immune to that disease. In this way most 

 persons have acquired immunity to certain common diseases. 

 It is known that each kind of toxin leads to the formation 

 of a specific anti-body which serves as an antidote for that 

 poison. Many of these toxins are complex and highly specific 

 substances, and yet the living organism, if given sufficient 

 time, can make a specific antidote for each particular kind 

 of toxin. What chemist by the use of his intelligence could 

 do anything approaching what his unconscious cells are able 

 to do in this respect? 



Internal regulation is frequently the result of the action 

 of certain internal secretions, or hormones: Thus the ability 

 to "nerve oneself" for a great effort involves many cor- 

 related adjustments, such as increase of heart beat, of blood 

 pressure, of respiration, and of muscular energy, and all of 

 these are caused by setting free into the blood "adrenin," 

 which is secreted by the adrenal gland; even the coagula- 

 bility of the blood is increased by this hormone. The adap- 

 tive character of all these reactions can be readily appreci- 

 ated when it is realized that these are just the conditions 

 needed in fight or flight, and in life and death struggles. It is 

 probable that many regulations of development are depen- 



