CHAPTER VII. 



INFECTION. 



THE spread of infection is influenced by: 1. The 

 number of species of animals subject to infection. 



Many human infectious diseases do not occur in ani- 

 mals, and many animal infections are not found in man. 

 Thus, so far as we know, gonorrhoea, syphilis, measles, 

 smallpox, typhoid fever, etc., do not occur in animals 

 under ordinary conditions; while tuberculosis, anthrax, 

 glanders, hydrophobia, and some other diseases are 

 common to both man and animals. 



2. The quantity of the infectious material thrown off 

 from the body and the prevalence of the disease. 



In diphtheria, typhoid fever, cholera, pulmonary 

 tuberculosis, septic endometritis, influenza, and gonor- 

 rhoea enormous numbers of infectious bacteria are cast 

 off through the discharges from the mouth, intestines, 

 and genito urinary secretions, causing great danger of 

 infection. On the other hand, in tubercular perito- 

 nitis, cerebro- spinal meningitis, septic endocarditis, 

 gonorrhoeal rheumatism and the like, there is little or 

 no danger of infecting others, as few or no bacteria are 

 cast off. 



3. The resistance of the infectious bacteria to the 

 deleterious effects of drying, light, heat, etc. 



In this case the presence or absence of spores is of 

 the greatest importance. The spore-bearing bacilli, 



