STAINING OF TUBERCLE BACILLI IN TISSUES. 167 



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 hard- 

 ening fluids, Miiller's, 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 per cent., as 

 preservative. Several drops of this are placed on a 

 slide, a section laid on top, and the slide 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 section, 

 which will lie perfectly flat and smooth on the surface 

 of the gelatin solution. The slide is then removed 

 from the oven and the surplus fluid poured from it, 

 thus bringing the section in contact with its surface, 

 after which it is set aside in a place protected from 

 dust, to remain until the section is firmly cemented to 

 it by the drying of the gelatin solution. The drying 

 may be hastened by keeping the slides in an oven 

 below the melting-point of the paraffin, but it is best 

 to set the slides aside until the next day, when the sec- 

 tions will be found to be perfectly cemented to them. 

 The paraffin is then removed from the section by tur- 

 pentine, the turpentine by absolute alcohol, the absolute 

 alcohol by 50 per cent, alcohol, and this by water, after 

 which the slides are placed in a 5 per cent, aqueous 

 solution of potassium bichromate for five minutes. 

 This renders the gelatin insoluble, and prevents the 

 sections from leaving the slides during their necessarily 



