2 Veterinary Medicine. 



are especially favorable to the reception and culture of such 

 microbes. Again, some may enter through the injured and 

 partly devitalized skin, and even in exceptional cases through 

 the sound integument. Very commonly however admission is 

 gained through wounds, abrasions, or other breaches of surface 

 of either mucosa or skin. These are very varied, but include 

 cuts, bruises, pricks, scratches, chaps, cracks, vesicles, pustules, 

 burns, frost bites, eschars, cauterizations, sloughs, the open um- 

 bilicus of the new-born, the wounds made by biting or stinging 

 insects, etc., the wounds made by external parasites or internal 

 worms, and those due to the poisons of venomous animals. The 

 action of insects in carrying infection from a diseased animal or 

 product to a sound one, and the conveyance of germs on or in 

 the bodies of worms, which hook themselves to vascular surfaces, 

 or migrate inward through the membrane, deserve especial men- 

 tion as these factors have been so much forgotten and overlooked. 



Certain microbes pass from the circulation of the dam to that 

 of the foetus, with or without colonization and disease of the 

 chorion. Others fail to pass through the placenta to the foetus. 



Some microbes (bacillus tetani, bacillus of emphysematous 

 anthrax) are confined to the seat of inoculation and perish in the 

 blood. 



Anierobes grow only in the depth of the tissues, where exu- 

 dation has diminished or arrested the circulation of oxygenated 

 blood. They die in the blood. Probes grow on or near the 

 surface, in the oxygenated blood, or where uncombined oxygen 

 is present. Some therefore enter most easily by surf ace wounds, 

 and some by deep wounds only. 



Again some genera and species are immune to certain microbes 

 so that an inoculation is harmless to them ; the microbes cannot 

 live and form colonies. Animals of susceptible species which 

 have passed through a self-limiting microbian disease show a 

 similar immunity. Some may carry the infecting germ on the 

 surface of the skin or mucosa, and transmit it to other (suscep- 

 tible) animals, though themselves immune. 



Colonization of Different Tissues. 



Certain microbes and their products show a particular affinity 

 for given tissues which they colonize tb the exclusion of others, 



