PKACTICAL HISTOLOGY TOil MKDICAL STUDENTS. 15 



hardening the retina and epithelium, hardens the tissue in 

 a day or two ; when hardened, place in distilled water for a 

 few days. Mount in saturated solution of potassium acetate. 



B. Hoio to Soften Tissues. — Bone and tooth maybe softened 

 in 2 parts nitric acid, 1 part chromic acid, 100 parts 

 water. A large quantity of this fluid always necessary. 

 It is sometimes desirable to soften or dissolve various con- 

 nective substances, such as white fibrous tissue, the cement 

 which connects the fibres of the lens and the fibrils of striped 

 muscle. White fibrous tissues may be softened in boiling 

 water. This is useful for coarse dissections of muscle. 2nd. 

 By maceration, at a temperature of 116° Fah., in dilute 

 sulphuric acid (1-lOth per cent.), ord. By maceration in 

 glycerine (1 oz.), and glacial acetic acid (5 drops), (Beale). 

 This is invaluable for enabling us to trace the endings of nerves 

 in many tissues. (See Beale, ' How to Work with the Micro- 

 scope.') The cement between the fibrils of the nerve axial 

 cylinder may be dissolved by 1st, maceration in the above acid 

 glycerine (Beale). 2nd, by maceration in iodised serum 

 (Schultze). The cement joining the fibrils of striated muscle 

 may be dissolved by maceration in dilute nitric acid (1 acid, 

 4 water). The cement connecting the fibres of the lens may 

 be dissolved by boiling for five or ten minutes in dilute sul- 

 phuric acid (1 per cent.). 



Separation of Tissue Elements. — 1. By dissection Avith 

 needles in handles. 2. By pressure. The separation is facili- 

 tated by the above-mentioned processes for softening and 

 dissolving connecting substances. 



Hoio to Make Sections of Tissues. — Some tissues are too 

 soft, others are too hard, to permit of sections being readily 

 made. Harden or soften in the above-mentioned ways. 

 Sections of softened bones and teeth made with a fine cir- 

 cular or straight saw. The sections are then ground suffi- 

 ciently thin upon a hone. Valentin's knife and scissors useful 

 for cutting soft tissues, such as liver, lung, and kidney. 

 Cartilage, or any tissue which by softening or by hardening 

 has been brought to a density somewhat resembling it, is cut 

 most readily by means of a scalpel or a razor. Cutting in- 

 struments must always be wetted. 1. Water. 2. Salt solu- 

 tion. 3. Methylated spirit. 4. Absolute alcohol are used 

 for this purpose. 3 and 4 are the best, but they are only 

 to be used in cases where spirit may be added to the tissue 

 without altering it — e.g., Avhen the tissue has been hardened 

 in spuit or chromic acid. The piece of tissue is often so 

 small that it is impossible to hold it in the hand, and it is 

 sometimes so brittle that it is apt to go to pieces when cut. To 



