156 BOVINE PATHOLOGY. 



concentrated state, and is therefore very useful for inocu- 

 lation purposes. The virus is thus thrown off from the 

 system, so that generally these diseases have a benign 

 character but under defective sanitary arrangements, and in 

 animals with vitiated constitutions, they may become 

 malignant, and highly destructive. In all of these dis- 

 orders we see a well-marked incubative stage, a period of 

 invasion, an eruptive stage, and, lastly, the stage of 

 repair. It is noticed that certain specific poisons are 

 eliminated by certain membranes, and in special ways. 

 We cannot explain this any more than why particular 

 medicinal agents act on special organs. The nature of 

 the contagium is still obscure; by some it is considered 

 to be corpuscular, by others bacterian. These diseases 

 are little influenced by medicinal treatment, but may be 

 altered very much for the worse by neglect of sanitary 

 precautions. Then we see considerable and permanent dis- 

 organisation of structure, complications tending to render 

 the animal useless, even if it recover. The eruption 

 must be encouraged in every possible way, and its various 

 changes promoted. The animaPs strength must be sup- 

 ported. Measures of isolation and disinfection are 

 essential. These diseases, especially vaccinia, derive great 

 interest and importance in their relations to diseases of 

 other animals. 



Vaccinia, Cow-pox, Yariola Yaccinia [with which are 

 noticed Varicella^ vel Vaccinoides, and Smallpox in cattle], 

 Yariolas constitute a class of diseases, one form being 

 peculiar to each species of animal ; thus, the eruptions of 

 this nature which occur in our domesticated animals and 

 in man are not identical, but only allied. Equine and 

 bovine variolae are sometimes considered exceptions to this 

 rule. Jenner observed that milkmaids took this disorder 

 from milking cows affected with it, and were thereby 

 exempt from smallpox, so he originated the system of vacci- 

 nation to the great and lasting benefit of mankind. The 

 same observer also assented to an observation of a con- 

 temporary of his (Dr. Loy), that the disease vulgarly 

 known as " grease '^ in the horse, also termed eczema 



