356 AGRICULTURAL BACTERIOLOGY. 



special change, but eventually running down and requiring 

 slaughter. In other cases the disease runs its course very 

 rapidly. When it infects the intestinal tract it may affect many 

 glands at once, and produce great numbers of small tubercles 

 in the intestinal organs, which look like masses of grapes, 

 and have given rise to the name grape disease, called Perlsucht 

 by the Germans. In S4jch cases the progress of the disease is 

 very rapid. If it attacks the lungs it will produce coughing 

 and difficulty in breathing. These various types, however, 

 concern the veterinarian rather than the bacteriologist. From 

 the bacteriological standpoint they are all the same disease, 

 produced by the same bacillus, differing only in the point of 

 attack, the violence of the pathogenic action and the rapidity 

 of distribution through the body. 



METHODS OF DISTRIBUTION. 



It is a fact of the greatest importance, now admitted on all 

 sides, that tuberculosis is contagious. By this is meant that 

 the relation of the bacillus to the animal is such that there is 

 an easy means of communication between one animal and an- 

 other under the ordinary conditions of life. The knowledge 

 of this fact in regard to human consumption has been of great 

 value, since it has been followed by a steady decline in the 

 amount of the disease. Such knowledge has not yet reduced 

 the amount of bovine tuberculosis. 



We can easily understand the methods of contagion when 

 we remember that the bacilli are discharged from any of the 

 open tubercles in the body and may readily find their way to 

 the exterior. If the disease is located in an internal lymphatic 

 gland it may not result in breaking down the gland, and there 

 may be no discharge. Under this condition there is no con- 

 tagion from this animal to another. But if it be located in the 

 lungs the bacilli will be discharged and pass through the 

 trachea into the mouth. They will enter the mouth and nasal 



