NORMAL TEMPERATURE 



157 



111 view of these normal temperature variations, which 

 often exceed the tubercuhn reaction, it is obvious that before 

 applying the test the normal temperature of the animals should 

 be approximately determined and that when they are being sub- 

 jected to the test they should be cautiously protected, other- 

 wise the comparatively slight elevation necessary to detect the 

 disease may be disguised. 



Fig. 34. Chart showing the effect of drinliing cold -water upon the tem- 

 perature of a cow. 



As the reaction seems to be the result of an affinity exist- 

 ing between the tuberculin and the living tuberculous lesion, 

 it is natural to suppose that when the two are brought together 

 in the same animal it would invariabl}- take place. Experi- 

 ence has shown that it almost always does. It is important to 

 understand, as far as possible, the reason for the exceptions 

 and the extent to which they occur. The reported failures of 

 the tuberculin tests fall into two distinct classes : 



( i) When there is a reaction and no disease is found. In 

 explaining this alleged error, the records of the cases which 

 have come to my attention have been so deficient in data con- 

 cerning the normal temperature variation of the animals, and 

 the incompleteness of the post-mortem examinations, that it 

 seems possible for the error to rest with the observer quite as 

 much as with the tuberculin. Unfortunately we are as yet 

 unable to determine, by the reaction, the extent of the disease, 



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