PRINCIPLES OF VETERINARY SURGERY 177 



dead or attenuated cultures into the animal, gradually in- 

 creasing the virulence or dose of the bacteria, until the 

 animal is able to stand a dose which in the beginning would 

 have killed him. 



In the manufacture of anti-streptococcus serum, many 

 varieties of streptococcus are used. Such a serum is called 

 a "polyvalent" serum. 



The manner of measuring the amount of serum to be 

 injected into an animal is as follows : 



We first determine the amount of toxin necessary to 

 kill a guinea-pig of 250 grams weight. This is called the 

 "minimum lethal dose". The amount of antitoxin neces- 

 sary to neutralize 100 lethal doses is called a unit. A cubic 

 centimeter of diphtheria antitoxin contains 200 or 300 units. 

 A cubic centimeter of tetanus antitoxin may contain a 1000 

 units. 



Antibactericidal serums are not standardized. They are 

 either diluted or are mixed with some mild antiseptic, or 

 heated in order to attenuate the bacteria. 



By the method of vaccination we usually inocu- 

 late a small dose of the bacteria themselves or a fairly large 

 dose of toxin into the animal, thereby giving the animal 

 a mild attack of the disease. He thus produces his own 

 antitoxins. 



PRACTICAL VALUE OF THE VARIOUS SER- 

 UMS. — As curative, prophylactic and diagnostic means, 

 the serums are valuable in the following diseases : An- 

 thrax, glanders, tuberculosis, cattle plague, Texas fever, 

 symptomatic anthrax, swine erysipelas, swine plague, hog 

 cholera, sheep and cow-pox, foot and mouth disease, dis- 

 temper, gangrenous septicaemia, streptococcus and staphy- 

 lococcus infections and many others. These serums are 

 also used in malignant diseases caused by cancers and ollitr 

 tumors. 



