ANIMAL BREEDING 201 



cities. Again, most individuals have at one time or 

 another experienced a feeling of discomfort when 

 together with a number of people in a poorly venti- 

 lated room or hall. This discomfort may in part be 

 due to the accumulation of small quantities of cytost 

 in the air of the room ; and if this be true, it is obvious 

 that the greater the number of people in the room the 

 more rapidly will such an accumulation take place. 



We have no direct evidence that humans actually 

 discharge cytost into the air, but that they must give 

 off something which is characteristically human is 

 evidenced by the fact that bloodhounds can trail a 

 man; and that many other animals, such as the deer, 

 can scent a human at some distance, providing the 

 wind is in their direction. Indeed, many animals ex- 

 hibit a remarkable sense of smell, which enables them 

 to seek their own kind. Since, as has been shown previ- 

 ously, cytost is distinctly species specific in its action, 

 it is conceivable that such species specific scent as is 

 shown by the dog is in part due to a special sensitivity 

 to cytost rather than to a sense of smell as we ordi- 

 narily understand it. 



The foregoing discussion, although admittedly 

 somewhat speculative, suggests that the animal 

 breeder should utilize every means at his disposal to 

 combat the action of cytost upon his animals. Aside 

 from the selection of an adequate diet, the prevention 

 of overcrowding, the preservation of cleanliness, and 

 the provision for adequate exercise, it is conceivable 

 that the professional breeder might profitably con- 

 sider the possibility of immunizing his animals to 

 homologous cytost. By so doing he might be able to 

 lower the mortality rate of his breeding stock and of 



