248 MACERATION, DIGESTION, AND CORROSION. 



methyl alcohol, and 20 parts of distilled water. Macerate for 

 several days (perfectly fresh tissue). 



536. GAGE'S Picric Alcohol (Proc. Amer. Soc. of Microscopists, 

 1890, p. 120). Ninety-five per cent, alcohol, 250 parts ; water, 

 750 ; picric acid, 1. Kecommended especially for epithelia and 

 muscle. A few hours suffice. 



537. Chloral Hydrate. In not too strong solution, from 2 to 5 per 

 cent, for instance, chloral hydrate is a mild macerating agent that 

 admirably preserves delicate elements. LAVDOWSKY (Arch. mik. 

 Anat., 1876, p. 359) recommends it greatly for salivary glands, 

 HICKSON (Quart. Journ. Mic. Sci., 1885, p. 244) for the retina of 

 Arthropods. 



538. Lysol (REINKE, Anat. Anz., viii, 1892, p. 582).- -Ten 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. 



539. 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 carbo- 

 hydrates 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. 



540. 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 grs. of coagulated 

 white of egg. 



