EXPERIMENT STATION BULLETINS. 563- 



be more readily detected, but unfortunately our knowledge has not yet 

 reached a point where absolute reliability is assured. 



By a response to tuberculin or a reaction we understand that a rise 

 of temperature has been produced by the injection of tuberculin in a 

 tuberculous animal and that a febrile condition exists in the animal. 

 It is this response to tuberculin which enables us to decide whether 

 an animal has tuberculosis or not. Should there be the slightest rise in 

 temperature or a very marked rise in temperature that is due to tubercu- 

 lin, tuberculosis is probably indicated. On the other hand, a rise of tem- 

 perature may occur from some other cause than tuberculin, when 

 it is expected that it will result from tuberculin only. Our investi- 

 gations thus far establish the possible variations which may occur in the 

 normal temperatures from various unknown causes, consequently we are 

 not in a position to state whether this rise of temperature is produced by 

 tuberculin or by some other agent. Errors are likely to occur and will 

 happen even to the extent, perhaps, of fifteen per cent, in some herds, but 

 usually the errors will be much less. If a herd is to be freed from tuber- 

 culosis, the errors will have to be controlled by a cautious study of each 

 animal's normal temperatures, and then, although the errors may be 

 greatly lessened, a small per cent, will still persist. 



There are characteristics which will assist us in deciding whether a 

 rise of temperature is attributable to tuberculin: 



First, There is a gradual rise of temperature beginning eight to six- 

 teen hours after injection; 



Second, This rise reaches the maximal point in a few hours, then grad- 

 ually falls back to normal; 



Third, This febrile condition persists through several hours; 



Fourth, The extent of rise may be measured by one or more degrees 

 which cannot be fixed and must be considered in connection with other 

 features; 



Fifth, There is sometimes an irregular febrile condition, which is diffi- 

 cult to interpret. This condition is more likely to take place in animals 

 much advanced in tuberculosis, yet it is by no means generally true. 



These statements are based upon the tables and are drawn from those 

 numbers marked with a +. In reviewing the numbers thus marked it 

 must be remembered that in some cases there is no reaction at all and 

 that it means, the animal had once responded but had failed in that 

 particular test, for it is established beyond dispute and long recognized 

 that cattle will not respond to tests made every six months or every year, 

 although they had reacted previously. 



The errors which may creep in even by recognizing the above character- 

 istics should be mentioned. Each characteristic is not infallible, it simply 

 is the best guide we are able to give. Turn to Table XVI, Nos. 6 and 17, 

 and there will be found what would be considered tyx>ical reactions. 

 Others are present in the tables. Such "normal reactions" cannot be 

 differentiated from "tuberculin reactions." 



So far as a close analysis of reactions is concerned, it scarcely seems 

 necessary to make one after the extensive study of normal temperatures, 

 and the designation of reactions in the tables. If the temperatures before 

 the injection of tuberculin are understood, the temperatures after injec- 

 tion will be easily interpreted. 



