Biological Therapy 



177 



is dissolved. Most satisfactory results from the ophthalmic 

 test are obtained when one disc is used in the manner de- 

 scribed to sensitize the eye, and in forty-eight to seventy-two 

 hours placing one or two additional discs in the same eye. 



The discharge of varying amounts of pus from the 

 injected eye constitutes a reaction. This reaction is gener- 

 ally written as Negative when no pus is apparent, or as 

 P-1, P-2, P-3 and P-4, depending upon the amount of dis- 

 charge present. Animals subjected to the ophthalmic test 

 should be observed each twenty-four hours up to and 

 including the seventy-second hour. 



COMBINATION TESTS. Formerly the only test offi- 

 cially recognized was the subcutaneous test. The United 

 States Live Stock Sanitary Association and the Bureau of 

 Animal Industry have officially endorsed so-called combina- 

 tion tests, and in the future, before being accredited, herds 

 must be subjected to a final combination test. This combina- 

 tion test may include any two of the above mentioned tests. 

 These combination tests are desirable since it has been 

 demonstrated that all three tests are reliable and that the 

 ophthalmic or intradermal tests frequently detect tuberculous 

 animals which fail to react to the subcutaneous test. 



It is of interest to note that if an animal reacts to the 

 ophthalmic or intradermal tests and later is subjected to the 

 subcutaneous test, a second local reaction of the eye or 

 dermis is frequently observed. 



The subcutaneous test is of limited value in cases of 

 advanced or generalized tuberculosis, and in animals which 

 have been repeatedly injected with tuberculin (so-called 

 "plugged" cattle). In these cases physical examination and 

 the other two tests furnish a means of detecting the affected 

 animal. Excellent results have been obtained in these cases 

 from the use of so-called "triple strength tuberculin," or by 

 using large doses of regular subcutaneous tuberculin. 



In retesting by the subcutaneous method at least six 

 weeks should elapse between tests. 



Uninformed persons sometimes claim that their cattle 

 contracted tuberculosis as a result of the injection of tuber- 

 culin. In order that this point may be correctly understood 

 and refuted the following brief description of the production 

 of tuberculin is offered. 



