BACTERIA IN CROUPOUS PNEUMONIA. 301 



agent common predisposing causes relating to the environment, acting upon 

 persons having various degrees of resisting power, induce attacks at various 

 intervals ; or it may be that in the presence of the specific cause and predis- 

 posing influences an exciting cause, such as exposure to cold, alcoholic ex- 

 cess, etc., is the immediate factor in the development of an attack. 



Without stopping to discuss further the facts relating to the epidemic 

 prevalence of the disease under consideration, I call attention to the well- 

 established fact that pneumonia prevails over a wide area of the inhabited 

 surface of the earth, and that by far the larger number of cases occur inde- 

 pendently of any recognized connection with previous cases, and often un- 

 der circumstances in which such connection can be very positively excluded. 

 And, on the other hand, the direct transmission of the disease by the sick to 

 those most closely associated with them, as nurses, etc., if it occurs at all, is 

 evidently a rare exception to the general rule. 



We must then conclude, as stated at the outset, that if pneumonia is a 

 specific infectious disease the microorganism which causes it is widely dis- 

 tributed. As a matter of fact, the pathogenic micrococcus which, from the 

 evidence now at hand, appears to be the specific etiological agent in acute 

 pneumonia has been found in the buccal secretions of healthy individuals 

 in various parts of the world in America, in France, in Italy, and in Ger- 

 many, and no doubt more extended researches will show that it is extremely 

 common. 



This statement may appear at the outset to make the view that the micro- 

 coccus in question is the cause of croupous pneumonia quite untenable. 

 For, it may be asked, how is it that the individuals who have this microor- 

 ganism in their buccal secretions escape an attack of pneumonia ? In the 

 present state of our knowledge this question no longer presents any serious 

 difficulties. We know, for example, that the pus organisms Staphylococcus 

 pyogenes aureus, albus, and citreus are very frequently found in the buc- 

 cal secretions and on the surface of the body of healthy individuals, and 

 that, although these micrococci are recognized as the cause of furuncles and 

 of all sorts of acute abscesses, they only give rise to the formation of such 

 abscesses under certain special conditions relating to the general health of 

 the individual, or to a traumatism by which their introduction to vulnerable 

 parts is effected. Again, the tetanus bacillus is a widely distributed micro- 

 organism which has been found in the earth, and especially in rich loam, in 

 various parts of the globe. But the hands of farmers and gardeners are con- 

 stantly soiled with such earth without their contracting tetanus. In this 

 instance it has long been recognized that a traumatism is an essential factor 

 in the chain of events which leads to the development of tetanus, and now 

 we believe, on satisfactory experimental evidence, that it is not the trauma- 

 tism per se, or the injury to the nerves, or exposure to cold, which in certain 

 cases gives rise to this infectious malady, but that the result depends upon 

 the introduction of a specific infectious agent at the time the wound was re- 

 ceived or subsequently the tetanus bacillus of Nicolaier. 



In the case of the tubercle bacillus, also, it is extremely probable, in the 

 light of our present knowledge, that this bacillus, in a living condition, not 

 infrequently finds a lodgment in the mouth, upon the Schneiderian mucous 

 membrane, or in the larger bronchial tubes of most individuals who live in 

 populous communities. Here also the infectious agent is only one factor, 

 although an essential one, in the production of the infectious disease. It 

 must be introduced to the vulnerable location, and must find a favorable 

 nidus in the tissues invaded. We have good reason to believe that in this, 

 as well as in other infectious diseases, there are wide differences, inhe- 

 rited or acquired, in the susceptibility of the tissues to invasion when the 

 infectious agent has been introduced to a favorable location. 



In a paper read before the Pathological Society of Philadelphia in April, 

 1885, in discussing the relation of my Micrococcus Pasteuri to croupous 

 pneumonia, I say: "It seems extremely probable that this micrococcus is 

 concerned in the etiology of croupous pneumonia, and that the infectious 



