NATURAL RESISTANCE AND FATIGUE 143 



In consequence, the observed variations in the re- 

 sponse to the wounds must be due to variations in the 

 natural resistance of the animals to wounds and the 

 sequelae thereof. 



In this connection it is interesting to note that, as 

 the author and others have observed, battered street 

 cats are usually better subjects than pampered house 

 cats for laboratory experiments which involve surgical 

 procedures. May we not conclude from this simple 

 observation that because of his fighting existence and 

 frequent bloody encounters, the alley cat's natural re- 

 sistance to traumatic injury has been significantly 

 raised above that of his brother, the protected house 

 cat? 



As has been shown in the previous chapters, the au- 

 thor's experiments upon shock produced in various 

 ways have all led to the conclusion that cytost, a prod- 

 uct of cellular disintegration, is the causative factor 

 primarily responsible for the train of physiological 

 changes which follow severe injuries. It seems, there- 

 fore, that individual differences in susceptibility to 

 shock — i.e., natural resistance to shock, must be in- 

 herently due to differences in susceptibility to cytost 

 — a concept in harmony with our observations relative 

 to the differences in response which normal animals 

 show upon injection of extracts of autolyzed tissue. 



As has been stated above, an animal's natural re- 

 sistance to a given environmental factor may be en- 

 hanced by appropriate stimulation by that factor at 

 an intensity lower than that required to inflict severe 

 injury. In the case of sunlight, the development of 

 colored pigments in the skin is a tangible explanation 

 of the increased resistance of the animal. On the other 



