100 THE DISEASES OF DOMESTIC AXIMALS. 



mon diseases in our cows, especially such as are grazed on road-sides 

 and house-yards. 



Traumata, wounds in the cutis, are very common among our 

 animals, and much more so among grazing animals, especially on 

 the feet and legs and around the hoofs ; and as these parts are fre- 

 quently in places where germs would be abundant (marshes, etc.), 

 they offer the most favorable atria to the penetration of germs. 



How do germs act ? 



By depriving the body of nutritive material, by obstruction, cap- 

 illary embolism, and by the products which either of themselves, 

 or by the disease-processes, are induced by them. 



That they require large quantities of oxygen has been made ap- 

 parent ; and it is self-evident that, on their entrance into the body, 

 there must be a constant struggle with the red blood-cells for this 

 necessary gas. Whether they produce carbonic-acid gas (CO a ), and 

 thus add to its accumulation in the system, is still an open question. 



That capillary embolism is possible has been too frequently ob- 

 served to be questioned. This condition would be but another way 

 by which parts, not the whole, of the system, are shut off from 

 oxygen and other nutritive material. 



Infectious diseases do not seem to last long enough to cause ne- 

 crosis, or necrobiosis (death), in parts thus shut off from the circula- 

 tion ; at least, never in my reading have I met with any description 

 of phenomena similar to those we meet with in ordinary embolism. 



When an organism withstands the invasion of an infectious dis- 

 ease, we may assume that it offers no longer a favorable condition to 

 the bacteria ; they die, suffer some sort of a dissolution, and are 

 passed off as an effete material. 



Disinfection. 



The birth of crude empiricism may be asserted to have been 

 coeval with the first realization of pain or suffering on the part of 

 man. The aim of modern medicine is prevention. We are ear- 

 nestly endeavoring to make practical the old saying, " An ounce of 

 prevention is worth a pound of cure." 



The men who boast of their " cures " are slowly becoming less 

 numerous among the true practitioners of medicine. 



As observers slowly came to the idea that one disease, and then 

 another, was due to some inficiens ; that many such diseases were 

 strictly or partly contagious — that is, passing directly from one ani- 

 mal organism to another — they began first to take means to prevent 

 them : hence restrictions of commerce, not only with regard to hu- 



