STAINING OF TUBERCLE BACILLI IN TISSUES. 173 



per cent, sulphuric acid, then in 70 per cent, alcohol, 

 and from this on as by the Ehrlich method. 



Dry method. For tubercle bacilli, as for many other 

 organisms in tissues, the following method may be 

 employed if only the presence of organisms is to be 

 detected and the histological condition of the tissues is 

 a matter of no consequence: bring the sections from 

 water upon a slide or cover-slip, dry, fix, and stain by 

 the methods for cover-slip preparations. 



Gray's method. The method employed by Gray at 

 the Army Medical Museum, Washington, D. C., a de- 

 scription of which is given by Borden, is as follows : 

 the tissue to be stained should be hardened, preferably 

 in alcohol, in pieces not exceeding 1.5 by 1.5 by 1 cm. 

 in size, though tissues hardened by any other of the 

 regular methods can be stained. Alcohol is to be pre- 

 ferred, however, as after its use the bacilli stain more 

 quickly and brilliantly than when one of the other 

 hardening fluids Mulleins, for instance is employed. 



After the tissue has been hardened it is imbedded in 

 paraffin, and cut in the usual manner. The sections 

 are then cemented to the slides with a filtered J per cent, 

 solution of gold-label gelatin, to which is added chloral 

 hydrate in the proportion of 1 percent., as a preservative. 

 Several drops of this are placed on each slide, a section 

 laid on top, and the slides placed in a warming-oven 

 kept at a temperature slightly below the melting-point 

 of the paraffin. In about five minutes all wrinkles will 

 have been taken out of the sections, which will lie per- 

 fectly flat and smooth on the surface of the gelatin solu- 

 tion. The slides are then removed from the oven and 

 the surplus fluid poured from them, thus bringing the 

 sections in contact with their surface, after which they 



