vm SECTION-CUTTING 137 



tissues i.e., quickly killing and coagulating the protoplasm 

 of the cells with a minimum of shrinkage, and of these the 

 one most generally useful is a solution of corrosive sublimate 

 (see a, above), in which, from a freshly-killed frog, place 

 small pieces of the various organs and tissues to be examined 

 e.g., skin, intestine, stomach, liver, pancreas, kidney, 

 ovary, spermary, and spinal cord, as well as the inner half 

 of the eye-ball. The intestine and stomach should be first 

 washed out in salt solution, and then cut into pieces about 

 J inch long ; the liver should be cut into pieces not more 

 than J inch cube. After about half-an-hour to two hours, 

 according to the size of the piece, place in water under a tap, 

 and wash thoroughly for a quarter of an hour or more, until 

 the corrosive sublimate is removed. 



After washing, transfer to 50 per cent, alcohol for a few 

 hours, and then to 70 per cent, for twenty-four hours, after 

 which the pieces may be stained at once (see below), or 

 transferred to strong methylated spirit (90-93 per cent.), 

 in which they may be kept until wanted. This completes 

 the process of hardening : it is done gradually, by alcohols of 

 increasing strength, in order to avoid shrinkage. 



In order to decalcify such tissues as bone, from which the 

 lime-salts must be extracted before cutting into sections, 

 place a small piece for a few days in 70 per cent, alcohol to 

 which 2 per cent, of strong nitric acid has been added : then 

 wash thoroughly, transfer to alcohol, and stain. 



b. Staining. Place the organs, cut into convenient sizes 

 for imbedding i.e., not more than J inch long, and, in the 

 case of such organs as the liver, J inch in thickness into 

 borax-carmine or haematoxylin for one or two days or even 

 more. They will become stained throughout, and the 

 difficulty of staining the sections after cutting will thus be 

 avoided. After staining, place them in weak alcohol (50-70 

 per cent.), slightly acidulated with hydrochloric acid : if a 

 watch-glass or some such vessel is used, it is sufficient to dip 

 the end of a glass rod into acid and stir it round in the alcohol. 

 The effect of the acid is to remove much of the colour from 

 the protoplasm of the cells, leaving the nuclei brightly 

 tinted. After half-an-hour or less in the acid alcohol, place 

 the tissues once more in strong methylated spirit. 



c. Dehydrating. Transfer from the strong methylated 

 spirit to absolute alcohol, which must be kept in a stoppered 

 or tightly corked bottle, as it will otherwise deteriorate by 

 absorption of water from the air. It has the effect of with- 

 drawing the last traces of water from the tissues, an abso- 



