276 GHAPTEB XXIII. 



agent tliat admirably preserves delicate elements. Lavdow- 

 SKY {Arch. mih. Anat., 1876, p. 359) recommends it greatly 

 for salivary glands, Hickson {Quart. Journ. Mic. Sci., 1885, 

 p. 244) for the retina of Arthropods. 



546. Lysol (Reinke, Anat. Anz., viii, 1892, p. 582).— 10 

 per cent, solution in distilled water or in water with alcohol 

 and glycerin. Spermatozoa of the rat or cortical cells of 

 hairs are said to be resolved into fibrils in a few minutes, 

 epithelial cells of salamandra to be dissociated instantaneously. 



Digestion. 



547. Digestion is maceration in organic juices, which by 

 dissolving out some of the constituents of tissues earlier than 

 others serves to isolate those which resist. The chief liquids 

 employed are gastric juice (or pepsin) and pancreatic juice 

 (pancreatin or trypsin). 



Pepsin is best employed in acidified solution, pancreatin 

 in alkaline. 



The most favourable temperature for digestion is about 

 40° C. 



Pepsin digests albuminoids, collagen substance and mucin, 

 more or less readily, elastin more slowly. Nuclein is either 

 not dissolved or very slowly. Keratin, neurokeratin, chitin, 

 fat and carbohydrates are not attacked. 



Pancreatin (trypsin) digests albuminoids, nuclein, mucin, 

 and elastic tissue ; whilst collagen substance, reticular 

 tissue, chitin, horny substances, fat and carbohydrates are 

 not attacked. 



Tissues for digestion should be fresh, or fixed with alcohol, 

 not with chromic acid or other salts of the heavy metals. 



548. Pepsin (Beale's, Archives of Medicine, i, 1858, pp- 

 296 — 316). — The mucus expressed from the stomach glands 

 of the pig is rapidly dried on glass plates, powdered, and kept 

 in stoppered bottles. Eight tenths of a grain will dissolve 

 100 grains of coagulated white of egg. 



To prepare the digestion fluid, the powder is dissolved in 

 distilled water, and the solution filtered. Or the powder may 

 be dissolved in glycerin. The tissues to be digested may be 



