MILK-BORNE INFECTIONS 



453 



weather, fatigue, use of cold drinking-water, etc. The ocular 

 method is also used occasionally, and has the advantage over 



Fig. 192.— A tuberculin test outfit. (Ward and Haring, Bull. No. 199, Univ. 

 of California Agri. Exp. Sta.) 



other methods in that the observer can compare the normal, 

 untreated eye with the eye receiving the tuberculin treatment. 



Fig. 193. — Manner of injecting tuberculin. (Ward and Haring, Bull. No. 

 199, Univ. of California Agri. Exp. Sta.) 



The diagnostic value of tuberculin is variously stated to be 

 95 to 98 per cent, correct. There are several limitations to the 

 test. When the disease has reached the last stages animals may 



