456 HORSE, SWINE AND POULTRY DISEASES 



placed in pure kerosene at once, the sore well filled and the bandage 

 saturated with it. (Kan. B. 163.) 



Diagnosis. From what has already been said of the symptoms 

 exhibited by hogs eick of hog cholera, it will be recognized that at 

 the beginning of an outbreak in a herd it is a difficult matter to be 

 sure that hog cholera is actually present, for the outward symptoms 

 are not characteristic, but only such as might be expected in any 

 acute disease. The same may be said of some of the changes which 

 take place in the internal organs. It is therefore necessary to con- 

 sider all of the features of the disease before making a positive de- 

 cision concerning the presence or absence of hog cholera in a herd. 

 The important features of hog cholera are: 1. Contagiousness. 2. 

 Symptoms of severe illness, such as fever, weakness, loss of appetite, 

 and diarrhea. 3. Hemorrhagic spots in the internal organs or but- 

 ton-like ulcers in the intestines. If these characteristics are found 

 in a disease of hogs in this country, we may be reasonably certain 

 of the presence of hog cholera. (F. B. 379.) 



VACCINATION FOR CHOLERA. 



Immunity. It is a well recognized fact that where an animal 

 has recovered from a contagious disease, as sometimes happens, such 

 an animal is very unlikely to be attacked a second time by the same 

 disease, even when exposed to it with impunity. In other words, we 

 say that such an animal is no longer susceptible to that particular 

 disease, or, that it has become immune. What this immunity 

 consists of, and just how it is brought about, has been the subject of 

 much discussion and many theories have been evolved to account for 

 it which need not be taken up here. It is evident, however, that the 

 body fluids, blood and lymph for instance, in such an immune ani- 

 mal have acquired some property or substance which they did not 

 possess, or only to a limited degree, before being attacked with the 

 disease. It may be well to explain here that there are two forms of 

 immunity an active and a passive form. An active immunity is 

 developed where an animal has become infested with the disease- 

 producing organism itself (provided recovery takes place } as in such 

 cases the various body cells are stimulated to develop their own anti- 

 toxin and this form of immunity is the most permanent and for that 

 reason is the most desirable. Passive immunity is obtained by in- 

 jecting direct a quantity of the antitoxin and is relatively of short 

 duration, depending upon the rapidity of its elimination. Probably 

 the most familiar instances of these two types of immunity are those 

 occurring in the practice of human medicine in which the active 

 form is well illustrated in the vaccination against smallpox, while 

 the use of diphtheria antitoxin will illustrate the passive form. 



Hyper-Immunity. We have said that an animal recovered 

 from a contagious disease has developed an immunity ; such an ani- 

 mal, however, probably only possesses a sufficient amount of immu- 

 nity in its whole body to protect itself, and its serum, therefore, would 

 be of little value in small quantities for the immunizing of other ani- 

 mals. It has been found, however, that the immune animal can be 

 safely injected with enormous amounts of virulent blood (blood 



