98 THE DISEASES OF DOMESTIC AXIMALS. 



persion ; so that, under otherwise similar circumstances, one disease 

 may attack a far greater number of individuals than another. 



The Infection of the Animal Oeganism. 



Here, again, we find ourselves mostly upon a hypothetical foun- 

 dation. 



All is not gold that glitters ; so it will be with many of the 

 existing theories of fungi-infection ; but out of all we shall finally 

 winnow many facts. 



The penetration of germs into the body by means of an intact 

 outer cuticle may be looked upon as impossible. 



Whether they can also penetrate through the mucosa, and walls 

 of the capillaries of the intestinal or respiratory tracts, is also very 

 questionable. 



In anthracis pulmonum, a condition of the lungs due to the pres- 

 ence of coal-dust in the finest form, we find it accumulates in the 

 alveolae, but we find no proof of its gaining access to the circu- 

 lation ; the same is true in the so-called " grinder's pneumonia," 

 which is due to the presence of stone-dust in the lungs. 



In the intestinal canal we know, from our physiological studies, 

 that even the finest qualities of solid fats are incapable of absorp- 

 tion ; the action of the gall and pancreatic fluids is first necessary, 

 by which they are reduced to an emulsion. 



We are not, then, justified in assuming that bacteria gain access 

 to the living organism, either on account of their minuteness, or in 

 any passive way. Action on the part of the bacteria themselves 

 must play no secondary part in this phenomenon. 



To a passive entrance, or in fact to any entrance into the living 

 organism, the respiratory tract offers by far the most favorable op- 

 portunity. 



As may be known to many, the capillaries of the lungs are of an 

 extremely delicate nature ; they also dip into the alveoles ; that large 

 number of bacteria are taken up with the aspired air seems very 

 probable ; that very few, even in a profusely impregnated atmos- 

 phere, gain access to the air-cells of the lungs, must be also true ; 

 for the mucosa of the respiratory tract extends from the entrance of 

 the nostrils to the beginning of the infundibula, or conglomerate of 

 air-cells. The alveolae themselves have no mucosa. The viscid 

 nature of the covering of this membrane is of such a quality as to 

 warrant our assuming that the major part of such germs are caught 

 by it, and gradually find their way back to the pharynx by means 

 of the ciliary movement of the tracheal and bronchial epithelium. 



