34 



INFECTION AND IMMUNITY. 



c 



tion for certain tissues after they reach the interior 

 of the body. 



Sometimes it would appear that a particular 

 surface is predilected only because it is the area 

 which is most commonly exposed to infection. 

 Thus, syphilis is usually a venereal disease, al- 

 though on proper exposure chancres occur readily 

 on the lip, the mucous membranes of the mouth, 

 tonsils, or through wounds in the skin. Hence 

 the predilection of the primary sore for the geni- 

 tals is only apparent. Also the diphtheria bacillus 

 occasionally is inoculated into wounds on cutane- 

 ous surfaces and in the vagina. Some mucous 

 surfaces are protected against microbic invasion 

 by the character of their secretions, as in the cases 

 of the stomach and vagina (See under "Natural 

 Immunity"). 



In the so-called cryptogenetic infections the 

 atrium escapes detection. Certain micro-organisms 

 may enter the body without causing a discoverable 

 reaction at the point of entrance (plague). Ex- 

 perimentally it has been shown that tubercle ba- 

 cilli readily pass through the intestinal wall into 

 the mesenteric lymph glands without causing le- 

 sions of the intestines. Leucocytes may carry or- 

 ganisms through the intact surface of the intes- 

 tines into the deeper tissues, and possibly the same 

 process occurs in the lungs, particularly in rela- 

 tion to the tubercle bacillus ( !). 



skin. Infection through the skin commonly take? 

 place through wounds (tetanus, glanders, malig- 

 nant edema and purulent infections), although the 

 wound may be so small as not to be discoverable 

 (bubonic plague). "Insect-borne" diseases are 

 inoculated through the skin by the bites of the 



