78 MICROSCOPICAL TECHNIQUE. 



until a slide-full is obtained, when they are transferred, and balsam 

 and cover applied. By this method long series may be readily 

 handled. Glycerine is used only when the mounting medium is 

 glycerine ; in this case the knife is wet with glycerine. 



Paraffin Infiltration by Exhaustion."^— Mr. A. Pringle finds 

 that this system of embedding objects or tissues in paraffin is of 

 value in ordinary work. The advantages claimed are : — Great 

 celerity ; certain and complete infiltration ; certain removal of the 

 solvent ; absence of distortion of the tissue elements ; obviation 

 of necessity for prolonged heating of the objects ; possibility of 

 using the same paraffin over and over again ; pecuniary economy. 



The only apparatus required is a small, simple air-pump, with 

 its usual glass chamber. The plate of the air-pump is smeared 

 over with glycerine or lard ; over this is laid a sheet of india- 

 rubber, which is also smeared with glycerine or lard. For greater 

 convenience the air-pump should have near the plate, between the 

 air-inlet and the plate, a tap, which is to be closed after the air is 

 exhausted. If the paraffin-stove is large enough to admit the air- 

 pump, with or without its barrel, so much the better. If no stove 

 large enough for this is at hand, it may be well to remove the 

 wooden stand on which the plate is usually mounted. 



Any of the ordinary processes preparatory to the embedding 

 are available, but preference is given to chloroform for reasons that 

 will appear apparent as the process is described. The preparation 

 is now put into the melted paraffin, the dish containing it is placed 

 in the air-pump, and the air exhausted. So long as the bubbles 

 rise the pumping may be continued, but it is well, after a little 

 pumping, to let air into the receiver at least once. Of course, the 

 paraffin is to be kept melted the whole time. If the stove will 

 take the air-pump, the best way is to exhaust till the bubbles rise 

 in great numbers to let in the air, to exhaust again, and, turning 

 the tap suggested, to put the whole apparatus into the stove, where 

 it may be left for a few minutes. The air is let in once more, the 

 dish is removed from the pump, and put into the stove till the 

 bubbles have disappeared from the surface, when the process is 

 complete. After chloroform-preparation, the process takes fifteen 



* Journ. Pathol, and Bacterial. ., I., 1892, pp. 117 — J19. 



