NATURAL RESISTANCE AND FATIGUE 151 



course of the experiments the animal's resistance to 

 cytost must have been raised. 



These experiments, made many years ago, demon- 

 strate that it is possible to increase the resistance of an 

 animal to the breakdown products of its own tissues 

 and open the way to a fascinating field of investiga- 

 tion, — the production of such an increased resistance 

 by various experimental methods. This problem is of 

 importance because in the battle between animals and 

 their environment, the former are subjected to many 

 conditions which tend to cause tissue damage and the 

 consequent liberation of cytost. If the animal is not 

 more or less resistant to the action of the latter, he 

 will be subjected in a greater or lesser degree to the 

 various ailments which, as has been shown in previous 

 chapters, may be induced by the parenteral introduc- 

 tion of cytost. If such be the case, the animal will be 

 less suited than his more resistant brothers to cope with 

 the environment which nature presents to him. It fol- 

 lows, therefore, that an animal's resistance to cytost 

 is a factor of considerable importance in determining 

 his so-called natural resistance. In consequence, if one 

 is enabled to raise an animal's resistance to cytost, it 

 follows logically that we shall in some degree be able 

 to raise his natural resistance. In other words, we may 

 be able to increase the adaptation of a given animal to 

 his environment and thus in some measure cause his 

 earthly struggle for existence to be easier and, per- 

 haps, more pleasant. 



Resistance to fatigue may be regarded as one im- 

 portant aspect of natural resistance, for obviously the 

 more easily an animal is fatigued by his daily routine, 

 the less is his ability to cope with his environment. 



