108 JOHNKS DISEASE 



six weeks old, is autoclaved at iio° C. for twenty 

 minutes, and then evaporated at 80° to 90° C. to a tenth 

 of its volume. The fluid is now filtered and precipi- 

 tated with 95 per cent, alcohol ; the precipitation is 

 hastened by the addition of a small quantity of sodium 

 chloride. The fluid is now passed through filter-paper 

 and the precipitate scraped off and dried in vacuo. 

 The precipitate can be purified by repeating the pro- 

 cess. For use, the white precipitate is made up into a 

 I per cent, solution with sterile water. 



To carry out the test, a few drops are placed into 

 one of the eyes of the animal, and the other eye is 

 used as a control. The presence or absence of a reac- 

 tion is judged by the amount of conjunctival inflam- 

 mation produced in the treated eye. In a tubercular 

 animal this reaction may be well marked, and a muco- 

 purulent secretion may result for a few days. The 

 ophthalmic or eye test has been used for the detection 

 of tuberculosis in animals that have been inoculated 

 by fraudulent dealers with large doses of tuberculin 

 just before sale in order to prevent any reaction if tested 

 shortly afterwards in the ordinary way. The conjunc- 

 tival reaction is not prevented by a previous subcu- 

 taneous inoculation of tuberculin. 



Intradermal injections of tuberculin, which cause an 

 inflammation or thickening of the skin in tubercular 

 animals, have also been used, and a tuberculin prepared 

 with a non-irritant lanoline base may be given as an 

 inunction into sound or slightly scarified skin. These 

 methods, however, are not of practical value on a large 

 scale, having no advantages as primary tests over the 

 simple subcutaneous injection. 



It is often not necessary to use an autogenous vaccine 

 to produce a reaction. Man, suffering from certain 

 forms of leprosy, reacts to a human tuberculin if suffi- 



