44 CITY MILK SUPPLY 



by other tests and they regard it as being more easy to apply because the 

 necessity of taking temperatures before and after injection is obviated. 

 Haring and Bell find that like the subcutaneous test the intradermal 

 test does not always react in advanced cases but think that it will detect 

 more arrested cases and consider that the results of retests compare favor- 

 ably with those obtained by the subcutaneous method under similar con- 

 ditions. Repeated intradermal injections cause the animal to lose sensi- 

 tiveness to the test. An alcoholic tuberculin should be used in making 

 the test and the lack of a standard tuberculin of this sort is an impediment 

 it has to meet. 



The Ophthalmic Test. The ophthalmic test was first used on cattle 

 in 1907. McCampbell and White and others find that it has some value 

 for diagnosing tuberculous cattle. A tuberculin that does not contain 

 peptone, glycerin, or carbolic acid as T.O. tuberculin does, must be used. 

 To apply it the head of the animal is turned at an angle and 1 to 2 drops 

 of tuberculin are dropped from a hypodermic syringe right on the eyeball. 

 Then the closed eye is slightly massaged for several seconds. Reactions 

 usually set in by the eighth hour but may be delayed so that observations 

 should be made in the twelfth, eighteenth and twenty-fourth hours. A 

 positive result is indicated by watering of the eye, reddening of the con- 

 junctiva and dropsical swelling of the lid. A purulent exudate accumu- 

 lates later, at the inner corner of the eye and usually runs down into the 

 face. This dries up and drops off in a few hours. There is no thermal 

 reaction. The objection has been raised that decision as to whether or 

 not the test is positive depends on the opinion of the observer which in 

 slight reactions is liable to error. Other objections are, that rain may wash 

 out and obscure evidence of the reaction ; long hay may wipe off the exu- 

 date and exposure to wind and to bright sunshine causes unsatisfactory 

 results. The test is satisfactory only when the cattle can be kept tied 

 under shelter for at least 16 hr. Haring and Bell with tuberculin from 

 the Bureau of Animal Industry tested 139 cattle known to be reactors 

 and obtained positive results in every case. They record one case when 

 on autopsy a cow that failed to react either to the subcutaneous or the 

 intradermal test but did react to the ophthalmic test, proved to be 

 tuberculous. 



One reaction probably inhibits another for a period of 6 weeks to a 

 year and is most pronounced in animals that have not been tested recently 

 with tuberculin; however, cattle that have been so tested will give the 

 reaction but with reduced intensity. 



Value of the Tuberculin Test. In describing the several methods of 

 using tuberculin the attempt has been made to set forth plainly the 

 limitations it has as a diagnostic agent but it should be clearly understood 

 that in spite of them all it is wonderfully accurate and that when properly 

 used it is a very effective weapon wherewith to fight this terrible scourge 



