PHENOMENA OF INFECTION. 79 



racial peculiarity, can this be explained. Animals also 

 exhibit the same peculiarity in susceptibility to disease. 

 Among cattle, Jerseys are more susceptible to tuber- 

 culosis than other breeds. Dogs are practically immune 

 to it, a fact which probably explains the high position 

 dog-fat holds among the ignorant as a remedy for tuber- 

 culosis. At a laboratory at which the writer once 

 worked, and where many dogs were used for experi- 

 mental purposes, the janitor sold large quantities of 

 the fat to a local charlatan who in turn disposed of it as 

 a specific for consumption. It must not be supposed, 

 however, that racial immunity, such as is frequently 

 the case with individuals, is ever perfect. There are 

 always families and individuals whose immunity is 

 diminished by marriage and environment, and the 

 whole race is subject to those diseases which are inci- 

 dental to age. 



As the family partakes of the characteris- 

 Family. tics of the race, family predisposition is 



subject to the same general rules as de- 

 scribed for races, with the exception, that marriage 

 between members of different races by blending the 

 vital forces may either increase or decrease the power 

 to combat disease. A similar result follows the union 

 of persons of the same family; and the great danger 

 of a summation of highly susceptible strains has led, 

 in many states, to the wise enactment of a law against 

 consanguineous marriages. An extension of this law 



