88 AGRICULTURE OF AIAIXi;. 



animal will grow there and produce the disease, if these same 

 germs are grown in the laboratory through generation after gen- 

 eration they lose in some degree their ability to grow in living 

 animals. They do not grow as readily in living animals as 

 before they were grown in the laboratory. It is found that the 

 germs that have originated in human beings are not quite as 

 virulent in cattle as those grown in cattle. We find that these 

 germs grow in a great variety of animals, but as they grow in 

 different animals they acquire certain characteristics that are 

 peculiar to them in these animals, and so we get an attenuated 

 virus, as we say, either from human beings or by growing the 

 bacilli of bovine origin in the laboratory, through generations. 

 In these ways we get organisms that do not grow very readily in 

 cattle. Now briefly, we will say that this is the most promising 

 line of investigation for getting a virus for vaccinating to pre- 

 vent tuberculosis at the present time. A great many are work- 

 ing along this line. They are endeavoring to perfect this virus 

 so that it shall have just the right strength ; it must not be too 

 weak to protect the animal, it must be weak enough so that it 

 will not grow in the animal to any great extent. But it must 

 protect the animal so that the stronger virus of the natural infec- 

 tion will have no effect upon it. There has been a good deal of 

 success along this line of preventive inoculation. Veterinarians 

 the world over are expecting, with a good degree of reason, that 

 in the not distant future a method of protective inoculation will 

 be available, at such a price and with such safety to the animals 

 and human beings as will warrant its quite general use. When 

 we have said this, we have said practically all that may be said 

 in regard to the matter at the present time. 



Dr. Salmon, who was for over 20 years at the head of the 

 Bureau of Animal Industry, last month published a bulletin for 

 the Bureau on the subject of Bovine Tuberculosis, and in this 

 bulletin he has collected together the reports of the work that 

 has been done along this line the world over for the last 15 years 

 or more. In this bulletin he says : "The ablest veterinarians in 

 the world are confidently expecting that a practical and safe plan 

 of procedure will soon be developed." And then in conclusion 

 he says : "There is still much to learn about 'vaccines' and their 

 effect, and the owner of cattle will be wise to avoid their use 



