164 BOVINE TUBERCULOSIS 



symptoms of the particular disease with which they are asso- 

 ciated. The characteristics and symptoms of the germ dis- 

 eases were well known long before the causing bacteria were 

 discovered. 



During recent years the improved microscope has revealed 

 the fact that bacteria, so abundant outside the animal body, 

 also exist in it, especially when it is the seat of disease. 

 Further investigation has demonstrated that certain kinds of 

 bacteria are the cause of certain definite diseases. In no dis- 

 ease is the causal relation of bacteria more surely established 

 than in tuberculosis. The bacteria which cause tuberculosis 

 are very slender, elongated or rod-shaped organisms whose 

 length is several times as great as their diameter. They are 

 called tubercle bacilli. They are so small that it would require 

 from eight to ten thousand of them, placed end to end, to 

 measure an inch. 



LESIONS OF THE DISEASE 



Whenever tubercle bacilli gain entrance to the animal body, 

 and find a chance to develop, the result is the production of a 

 new growth in the tissues, in the form of a small, rounded 

 body called a tubercle ; from this fact the disease takes its 

 name of tuberculosis. When newly produced, the tubercles 

 are the size of a mustard seed or smaller ; they are harder than 

 the normal tissues and are readily detected by the sense of 

 touch. As the disease advances the tubercles increase in 

 number and may become massed together into larger nodules, 

 which are frequently very numerous and of all sizes from that 

 of the original tubercle up to that of the fist, or even larger. 

 Being poorly supplied with blood, the tuberculous tissue has 

 not the vitality of the normal tissues ; as a consequence it 

 has a tendency to degenerate or break down. When this has 

 taken place, the tubercle is found to contain a yellowish mate- 

 rial, sometimes dry and cheese-like, at other times semi-fluid 

 and pus-like ; in any advanced case such tubercles as these are 

 abundant. There is also frequently a deposit of lime in the 

 tubercles, which gives a gritty character to their contents. 

 The broken-down matter may remain enclosed in the tubercle 

 or may be absorbed, or it may break through its enclosing 



