406 HISTOLOGY. 



surrounding and infiltrating the tissue with a rirm substance which can 

 readily be cut into thin sections. Celloidin and paraffin are used, each 

 having its peculiar advantages. 



To imbed in celloidin one needs graded alcohols, a mixture of equal 

 parts of ether and absolute alcohol, a thin and a thick solution of celloidin. 

 and vulcanized fiber blocks of such size as can be clamped in the carrier of 

 the microtome. 



Thick celloidin consists of 30 grams of Schering's dry granular celloidin 

 dissolved in from 200 to 250 cc. of an equal mixture of ether and absolute 

 alcohol. It has a thick syrupy consistency and becomes constantly denser 

 as the ether evaporates. It should be kept in a tightly closed preserve jar. 

 Thin celloidin contains twice as much "ether and absolute" as the thick. 



The piece of hardened tissue is trimmed to the size and shape desired 

 and is put successively in 95 per cent., absolute, and absolute and ether, 

 remaining 24 hours in each. Then it is immersed in thin celloidin and 

 finally in thick celloidin, in each of which it stays from 24 hours to a week 

 or even longer. The success of the process depends largely upon the 

 thorough penetration of the celloidin into the tissue. The time required 

 in the celloidin varies with the penetrability of the tissue and the size of the 

 piece. After remaining in the thick celloidin long enough the tissue is 

 taken out with a mass of adherent celloidin and is pressed gently against 

 the roughened surface of a block of vulcanized fiber. The celloidin should 

 cover the tissue and spread out at its base upon the block. As soon as a 

 film has formed over its surface, the block and attached specimen are dropped 

 into 80 per cent, alcohol in which the mass becomes firm. It is ready for 

 sectioning in 6 hours. While the block is clamped in the sliding microtome 

 with which sections from 10 to 15 ;i should be cut, it is kept moistened with 

 80 per cent, alcohol; the knife also should be wet with the same. Sections 

 are immediately transferred to a dish of 80 per cent, alcohol in which they 

 unroll, and w r here they remain until it is desired to stain them. Each sec- 

 tion is surrounded by celloidin which it is not desirable to remove; the 

 sections would then be too fragile. Therefore they are not to be placed in 

 absolute alcohol. In case the tissue was not properly imbedded it may be 

 returned to ether and absolute, and again be put through the celloidins. 



To imbed in paraffin the block of hardened tissue is immersed for 

 from 6 to 12 hours in the following fluids successively: 95 per cent.; ab- 

 solute; a mixture of equal parts of chloroform and absolute; chloroform. 

 Then it is transferred to chloroform saturated with paraffin, which may be 

 kept warm by placing on top of the paraffin bath; in this mixture it re- 

 mains about 4 hours and then is put in melted paraffin. Hard paraffin 

 which melts at 50 is ordinarily used, but if this is brittle when cut into the 



