182 INFECTION AND IMMUNITY. 



of tetanus toxin, tetanic symptoms may appear. 

 In either case, there is some loss of weight and 

 often fever, and another injection must not be 

 given until the original weight is regained and 

 the general behavior of the animal indicates that 

 its former healthy condition is re-established. 



Several months of such treatment are necessary 

 for the production of diphtheria antitoxin in high 

 concentration. At the end of this time blood is 

 drawn from the jugular vein by means of a large 

 trochar to which a rubber tube is attached. The 

 tube leads to a tall glass cylinder holding from 

 one to two liters, and into this the blood is allowed 

 to flow. Six liters may be drawn safely from a 

 horse of average size. 4 The most rigid asepsis is 

 observed in taking the blood. The glass cylinders, 

 appropriately covered to prevent contamination, 

 are then set in a cool, dark place, and after the 

 serum has separated from the clot samples are 

 taken to be tested for their antitoxic value. 

 Preservatives The serum, in bulk or after being bottled for 

 the trade, is preserved at a low temperature and 

 in the dark, 0.5 per cent, of carbolic acid having 

 been added to insure sterility. The addition of 

 the acid may cause harmless cloudiness in the 

 serum, but does not destroy the antitoxin. Serums 

 may be preserved perfectly in a dried or frozen 

 state. 



Many facts of scientific and practical impor- 

 tance have been brought to light through the im- 

 munization of animals on a large scale. It has 



4. Some horses may be bled as many as forty times 

 without suffering a conspicuous deterioration in health. In 

 time, however, an animal becomes less valuable as an an- 

 titoxin producer. 



