40 CITY MILK SUPPLY 



"It has been found that either the human or bovine variety of tubercle bac- 

 teria can be used in the preparation of tuberculin. Occasionally a culture of 

 tubercle bacteria is found that will not produce satisfactory tuberculin. The 

 active principle of tuberculin is believed to come from the bodies of tubercle 

 organisms that have become macerated in the culture medium." 



The tuberculin above described is the original tuberculin of Koch and 

 is commonly marked T.O.; he later prepared a new tuberculin from the 

 bodies of unheated tubercle bacteria that is usually marked T.R. 



The dose of tuberculin is graduated to the size of the animal. That 

 given an adult animal of medium size is 0.25 c.c. of the T.O. That put up 

 in the laboratories of this country is so diluted that 2 c.c. is a dose. 



There are three different ways of using tuberculin to detect tubercu- 

 losis in cattle and they are distinguished as (1) the subcutaneous test, 

 (2) the intradermal test or von Pirquet reaction and (3) the ophthalmic 

 test. 



Subcutaneous Test. In the subcutaneous test the cattle are stabled, 

 watered and fed in the usual place and way. Since the temperature of 

 cattle varies, it is taken three times at 2- or 3-hr, intervals, previous to 

 injection. At 8 or 9 p.m. the tuberculin is administered beneath a fold 

 in the skin, commonly at the shoulder. Seven hours after injection the 

 taking of the rectal temperatures of the animals is commenced and obser- 

 vations are taken thereafter every 2 or 3 hr. until the twentieth hour after 

 injection. The usual reaction consists of a rise in temperature beginning 

 about the sixth or eighth hour after injection and continuing several hours. 

 The normal temperature of the cow is 101 to 102. 5F. and the tuberculin 

 causes a rise of from 1 to 5F. The interpretation of the thermal reaction 

 requires experience and good judgment. Some testers regard a rise 

 of 1.5 or 2 above the highest temperature recorded prior to injection 

 as positive. Moore, on the basis of many autopsies, believes that a slight 

 rise may represent a reaction; that if the curve is well-marked, the cases 

 are suspicious when the maximum temperature ranges from 103. 5F. 

 down to 103 or even to a few tenths of a degree less and that on slaughter 

 40 to 60 per cent, of these animals show tubercular lesions but that 104 

 is the minimum at which one can make a sure diagnosis. 



The tuberculin test has certain limitations. It will not detect tuber- 

 culosis in the prodromal stage, or in arrested cases, or sometimes in very 

 advanced cases and it may be vitiated by " plugging" that is by dosing 

 the animal with tuberculin previous to the test. Also poor tuberculin 

 or that which is too old is worthless. Since the test will not pick out the 

 animals coming down with the disease, nor those in which it is inactive, 

 it is imperative to retest a herd after 6 months or at most a year. Failure 

 to do so has led to disastrous results. The fact that the test does not 

 demonstrate animals of these classes has an important bearing on the 

 slaughter of animals in tainted herds and on the purchase of non-reacting 



