106 



CANADIAN FARM YEAR BOOK. 



Detection of Infected Animals 



"The detection of animals affected 

 with tuberculosis is rendered much 

 more difficult by the fact that ani- 

 mals may be suffering from this dis- 

 ease in quite advanced stages, and 

 to have been a source of infection to 

 the rest of the herd for a considerable 

 time, and yet not exhibit any outward 

 symptoms which would cause the 

 owner to suspect the presence of this 

 dreaded disease. A cough is not evi- 

 denced save where the lungs are af- 

 fected, and all the organs of the body 

 are liable to attack. The disease 

 will likely to have progressed to a 

 very advanced stage before such 

 symptoms as unthriftiness, loss of 

 flesh, and a general appearance of 

 lack of vigor will Arouse the sus- 

 picions of the attendant. 



Many of the symptoms that are re- 

 lied on by the human physician in 

 reaching his opinion are not avail- 

 able in examining cattle. The thick- 

 ness of the skin and of the chest 

 wall, for instance, makes it difficult 

 to detect a diseased condition of the 

 lungs by listening to the sounds made 

 in breathing, whereas this is compar- 

 atively easy in human beings. Sci- 

 ence has, however, discovered a test 

 by which the presence of this dis- 

 ease may be detected, even when no 

 outward symptoms are exhibited. 

 This is known as the tuberculin test, 

 because the substance used in making 

 it is called tuberculin. 



"Tuberculin does not harm healthy 

 cattle, even in large doses, but on 

 diseased animals it produces a 

 marked effect. This is shown by a 

 feverish attack, which comes on 

 about eight or twelve hours after the 

 tuberculin is administered, lasts a 

 few hours, and then subsides. This 

 temporary fever is called the reac- 

 tion, and animals which show it are 

 called reactors. The value of the test 

 lies in the fact that diseased animals 

 react while healthy ones do not. 



"The tuberculin test in the hands 

 of a competent and experienced man 

 is much more accurate than any 



other method of detecting tubercu- 

 losis. Tne records of a large number 

 of tests made by Government offi- 

 cials show that, with certain precau- 

 tions, it is accurate in 98 per cent. 

 of the reactions obtained. This gives 

 a margin of a possible 2 per cent, of 

 error, and this small number may be 

 still further lessened by care in mak- 

 ing the test. For practical purposes, 

 any animal which reacts must be con- 

 sidered tuberculous. 



"It must be recognized that there 

 are some limitations to the test as an 

 indicator of the presence of the dis- 

 ease. As has been stated, the indica- 

 tion given is by setting up a slight 

 feverish condition in a diseased ani- 

 mal; hence, it is quite apparent that 

 the test should not be applied to any 

 animal which, from any cause, may 

 be expected to show a slightly in- 

 creased temperature from causes 

 other than that brought about by the 

 injection of the tuuerculin serum. 

 The test should not be applied to 

 cows which have just calved, or are 

 about to calve, as the temperature 

 at this time is apt to vary consider- 

 ably from the normal. For the same 

 reason, the test should not be ap- 

 plied to cows about to enter upon the 

 period of oestrum. 



The test also fails to detect the 

 disease in animals very recently in- 

 fected. The disease has to make a 

 little progress before the test reveals 

 its presence; and in the beginning of 

 each case there is a period between 

 the entrance of the germs into the 

 body and the time when they will 

 have multiplied sufficiently for the 

 test to reveal their presence. This is 

 called the period of incubation, and 

 lasts from ten days to two months. 



"When the disease is far advanced 

 and the animal is wasting, the ani- 

 mal will frequently fail to show the 

 characteristic reaction indicating the 

 presence of the disease. This is not 

 of. much practical importance, as such 

 cases can generally be recognized 

 without the aid of tuberculin. 



