CHAPTER IX. 107 



(4) Trim the block, and fasten it on to the plate of a microtome 

 by means of some of the thick lead-gum (hardened afterwards in 

 ammonia vapour). Cut sections with an oblique knife, the block 

 being moistened with a solution 1 per cent, sodium chloride in 

 aq. dest. The sections are placed in the same solution, in which they 

 must not stay more than one hour. 



(5) Sticking the sections to the slide is done by a modification 

 of OLT'S method, 182. Cover the slide with albumen, then with 

 gelatin, arrange the sections, press down with a cloth, and harden 

 in formol vapour. See also J. A. Murray, below. 



(6) The lead-gum is then dissolved away in 5 per cent, acetic acid. 

 After washing you stain and mount in any way desired. 



Neither gum arabic (acacia), plum, nor apricot give quite such 

 good results as cherry gum. SALKIND recommends two fixatives to 

 precede this method of imbedding. 



A. Formol, acetic acid, sub-acetate of lead, 1 part each. Aq. 

 dest., 5 parts. 



B. Formol . . . . .10 c.c. 

 Acetone . . . . 30 ,, 



Water . . . . . 40 ,, 

 Citric acid . . . . 5 to 10 grms. 

 Saturated with Sudan III. 



After A, it is not necessary to wash out. After B, and the 

 majority of such fixatives as bichromate especially, you must wash 

 out in running water. 



J. A. MURRAY (Report of Imper. Cancer Bureau, 1919) fixes cartilage 

 in 10 per cent, formol-salt solution for at least twenty-four hours. 

 After Salkind's lead-gum imbedding, cuts sections 10 15 p thick with 

 sliding microtome. Transfers sections for from ten minutes to one hour 

 in 1 per cent. NaCl solution. Special slides prepared beforehand by 

 coating in 1 per cent, gelatin and allowing to dry. 



The prepared slide is immersed in the salt solution (NaCl), sections 

 arranged with a smooth-pointed glass rod, superfluous liquid drained 

 off, and a wetted cigarette paper carefully lowered over the sections. 

 Firm pressure with several layers of filter paper makes the sections 

 adhere to the slide. Withdraw the cigarette paper and expose to formol 

 vapour for a few minutes. Transfer to 10 per cent, formol five minutes, 

 then treat in the 5 per cent, acetic to remove the lead-gum. Stain. 



173. Joliet's Gum and Glycerin Method (Arch. Zool. Exper. et Gen., 

 x, 1882, p. xliii). Pure gum arabic dissolved in water to the consistency 

 of a thick syrup. Pour a little of the solution into a watch-glass, and 

 add from 6 to 10 drops of pure glycerin. In the winter or in rainy 

 weather less glycerin should be taken than in the summer or dry weather. 



The object is imbedded in the mass in the watch-glass and the whole 



