CONTROL OF INFECTIOUS DISEASES 86 1 



carrying the germs in their intestines (tetanus), by cows actually sick of 

 tuberculosis, or by other similar instances of disease derived directly 

 from preceding cases or carriers in the lower animals. 



Another class of cases where lower animals convey disease by biting, 

 and yet act merely mechanically is instanced by the septicaemia some- 

 times arising from bites of well animals (rats, snakes, mosquitoes, etc.), 

 the bite acting merely to admit to the tissues pathogenic forms acci- 

 dentally present in the animal's mouth or on the skin of the bitten 

 person. These must be distinguished from cases where the animal 

 transmits thus a disease from which it is itself suffering (as when a rabid 

 dog spreads rabies by biting other animals or man) and from true 

 poisoning by injection of animal products at the time of biting (as done 

 by poisonous snakes, mosquitoes, etc.). 



