ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



117 



walls g ; the sloping sides tend to minimize the pitting of the paraffin 

 block. 



An alternate method of utilizing organized structures so as to provide 

 directing marks in paraffin blocks is as follows : — A glass plate is smeared 

 evenly with a minimum of glycerin. A slab of bulk-stained tissue some 

 50 microns thick is deposited on the plate, some water is run under it, 



Fig. 21. 



and the plate is gently heated ; the water is drained off and the section 

 allowed to dry on. When required for reconstructive purposes, embed- 

 ding bars are set up on the plate, the paraffin section forming the floor. 

 The object is then embedded in the usual way, so that eventually a block 



. Fig. 22. 



with one covered surface is obtained. This face is then grooved with a 

 " Ritzer." No further treatment is required, and the block is cut in the 

 usual way, taking precautions to ensure that the grooves made by the 

 " Ritzer " shall be perpendicular to jfche cutting plane. 



(4) Staining- and Injecting - . 



Distinguishing Dead from Living Leucocytes.* — C. Achard finds 

 that when leucocytes are treated with neutral red, the living are un- 

 coloured or contain red-stained and intra-protoplasmic vacuoles or 

 granulations ; the nuclei of dead leucocytes stain red-brown, and there 

 is no intra-protoplasmic coloration. Two solutions are used, one is 

 normal saline with 6 per 1000 citrate of sodium, another is normal 



* Brit. Med. Journ. (1910) ii. p. 1416. 



