CHAPTER VI. 



AVENUES OF EXIT OF INFECTIOUS AGENTS 

 AND PARASITES FROM THE BODY. 



The source of every infectious disease is always 

 another infectious disease, that is to say, the infectious 

 agent has come directly or indirectly from some other 

 person. The spontaneous generation of disease is no 

 longer believed in, no more than is the spontaneous 

 generation of life from lifeless matter. It is true that 

 we cannot always trace the connection between suc- 

 cessive cases of the same disease, but such instances 

 are few in comparison with the number in which the 

 relationship can be proven. However, what has defi- 

 nitely been determined is the manner of exit from the 

 body of micro-organisms in practically all of the infec- 

 tious diseases of both known and unknown origin. 

 This, from a sanitary standpoint, is of surpassing 

 importance, because it permits of our destroying the 

 infectious agents at their source and when concentrated, 

 and thus give them no opportunity to be scattered, so 

 to speak, to the four winds. 



It is self-evident that the communicability of a 

 disease bears a definite relationship to the number of 



151 



