SECTION-CUTTINO. 185 



cut by turning the milled disk with the one hand and 

 causing the knife to traverse the tissue with the other. 

 The tissue and the knife-blade should be kept wet 

 with alcohol, so that the sections may float upon the 

 blade of the knife, from ^vhich they can easily be re- 

 moved, without tearing, A\ith a curved needle or a 

 xiamel's-hair brush. As the sections are cut they are 

 placed in a dish containing alcohol. 



There are some tissues which, by reason of their 

 histological structure, do not become sufficiently dense 

 when exposed to alcohol to permit of their being cut in 

 the above way. It becomes necessary to render them 

 more solid by filling their interstices with some sub- 

 stance that neither interferes with their structure nor 

 prevents their being cut into sections. They must be 

 " imbedded," as this process is called. 



Imbedding in eelloidin. Most convenient for this 

 purpose is eelloidin, a body somewhat similar to collo- 

 dion, soluble in a mixture of equal parts of alcohol and 

 ether, as well as in absolute alcohol. 



After hardening in alcohol the tissue to be imbedded 

 is placed in a mixture of equal parts of absolute alcohol 

 and ether and left there for twenty-four hours. It is 

 then transferred to eelloidin. Two solutions of eelloidin 

 are to be employed : the one a thin solution in a mixture 

 of equal parts of absolute alcohol and ether, the other a 

 thick solution in the same solvent. Into the thin solu- 

 tion, which should be of about the consistence of very 

 thin syrup, the tissue is placed from the absolute alcohol 

 and ether, and allowed to remain for twenty-four hours. 

 It is then placed in the thick solution for about a day. 

 When removed it should be placed immediately upon 

 a bit of cork or a block of wood. The adherent eel- 



