746 MODE OF SPREAD OF INFECTIVE DISEASES. 



disease in question coincides with the specific seat of 

 invasion. Erysipelas develops in the lymphatic channels 

 of the skin ; wounds of the skin which open an entrance 

 to these channels form the points of invasion of the 

 erysipelas cocci : gonorrhoea establishes itself only on 

 the urethral and conjunctival mucous membrane, and 

 these are likewise the seats of invasion of the gonococci : 

 pneumonia is limited to the lungs, and there the in- 

 vasion of the infective agents must begin : typhoid and 

 cholera localise themselves in the first place in the 

 intestine (leaving out of account the secondary deposits 

 of the typhoid bacilli), and here we must look for the 

 seats of invasion of the infective agents. If typhoid 

 bacilli are introduced into the lungs, pneumonia bacteria 

 into wounds in the skin, gonococci on the intestinal 

 mucous membrane, there is no result even when small 

 wounds and injuries are present. 



Some infective agents can set up a primary specific 

 disease in several different organs of the body ; for 

 example, anthrax in wounds of the skin, in the intestine, 

 in the lungs ; tuberculosis likewise in the lungs, 

 intestine, genito-urinary system, &c. ; diphtheria on 

 various mucous membranes. In the case of these 

 diseases the points at which the infective agents can 

 enter are therefore correspondingly more numerous. 



In the case of the acute exanthemata it is probable 

 that the skin or the surface of the mucous membranes 

 are the parts which are specially predisposed for the 

 development of the infective agents, and it is also pro- 

 bable that these parts are the seats of invasion of other 

 as yet unknown infective agents. 



These points We must next inquire whether these points of in- 

 pormlt th? vasion peculiar to the various kinds of infective agents 

 entrance of permit the establishment and development of these 



bacteria either L . , . 



when in a agents when the tissues are in the normal condition, or 

 normal n- ^^her solutions of continuity of the skin or mucous 

 membranes must be present to enable the infective agents 

 to penetrate. It is conceivable that some infective 

 agents do not require any preparation of the seat of 

 invasion, but only that they should be protected while 



