PORTALS OF ENTRY OF INFECTIOUS AGENTS. 171 



tions with which having occurred in laboratories by a 

 culture being unwittingly drawn up into the mouth. 

 But under natural conditions of infection, where only 

 casual contact between a patient and another person 

 takes place, how can we believe that very many germs 

 reach the throat through inhalation? Certainly they 

 are by far not so numerous in air as when grown in 

 cultures! Furthermore, in every disease, we concede 

 the co-operation of contributing or predisposing causes : 

 enlarged tonsils and adenoids in diphtheria; exposure 

 and alcoholism in pneumonia; indigestion, fatigue, 

 and over-ripe fruits, in cholera, etc. Why ? if the germs 

 acting alone are sufficient? 



Finally, only a limited number of persons exposed 

 to an infectious disease contract it, a fact which cannot 

 be explained in the case of local diseases on grounds of 

 greater general predisposition. In diphtheria, gonor- 

 rhoea, cholera, etc., might it not be because in those 

 persons that we say are susceptible, the predisposing 

 causes ultimately resolve themselves into invisible 

 breaks or ruptures in the continuity of mucous sur- 

 faces ? 



The subject of the inoculability of diseases has been 

 thus fully discussed because of our classification of the 

 portals of entry. We have endeavored to show that 

 our first group, "through wounds of skin or mucous 

 membranes," might be made to include practically all 

 diseases of known etiology. But such a division is 



