362 AGRICULTURAL AND INDUSTRIAL BACTERIOLOGY 



adopted by the U. S. Department of Agriculture is to 

 secure fresh muscle tissue in which the blackleg organism 

 has been growing, grinding this in a mortar and finally 

 squeezing out the fluid. This contains many of the organ- 

 isms, together with spores. This is spread in a thin layer 

 and dried to a brownish scale at blood heat. The vaccine is 

 prepared by mixing one part of this material with two parts 

 of water and placing in a hot air oven at a temperature of 

 from 95° to 99° c. for six hours. This heating attenuates 

 the organisms so that they may be injected without fatal 

 results into susceptible cattle. The vaccine in some cases is 

 suspended in water and is injected under the skin of ani- 

 mals to be immunized by means of a hypodermic syringe. 

 In other cases it is made up into tablets which are inserted 

 under the skin. In some cases, the vaccine is soaked on 

 threads which are drawn into tissues by means of a needle. 

 In general, vaccination against blackleg has proved satis- 

 factory. 



The complete life history of Clostndium chauvcei in 

 nature is not well understood. It seems probable that it 

 may under certain circumstances multiply in the alimentary 

 tract of suitable animals. It is certain that the organism 

 is present in some soils and not present in others. In some 

 cases the pastures of one farm or one part of the farm may 

 harbor the organisms, and such farms be subject to attacks 

 of blackleg, and adjoining farms may be entirely free. In 

 European countries it is well known that certain alpine pas- 

 tures cannot be grazed by young cattle which have not been 

 previously protected by vaccination against blackleg. 



Infection is believed usually to occur through wounds 

 and the disease is rarely if ever transmitted directly from 

 one animal to another. Commonly it is difficult to deter- 

 mine the manner in which the organism has gained en- 

 trance, that is, cryptic infections are comparatively com- 

 mon. It is believed that in such cases the organism may 



