Ch. XI] PREPARATIONS BY THE COLLODION METHOB 387 



The Collodion or Parlodion Method of Sectioning 



§ 624. Collodion method. — In this method the tissue is thor- 

 oughly permeated with a solution of collodion, which is afterward 

 hardened. Unlike the paraffin of the paraffin method, the collodion 

 (§ SSS^) is not subsequently removed from the tissue, but always 

 stays in the sections. It is transparent and does no harm. 



The fixing and dehydration with 95 % alcohol is the same as for the 

 paraffin method. 



The paraffin method gives thinner sections than the collodion 

 method and for series and large numbers of sections is superior. 



The collodion method requires no heat for infiltration, and it does 

 not render the firmer forms of connective tissue so hard and difficult 

 to cut. It is especially adapted for making sections of large pieces 

 of tissue or organs and when thick sections are desired. It is not 

 easy to cut sections less than 10 {j, with collodion, while with paraffin 

 it is possible to make good ribbons of small objects of dehcate texture 

 2 jLi to 3 jtt in thickness. With a very sharp knife and small dehcate 

 object, and one of the better forms of microtomes, one can cut short 

 paraffin series in. 1 fx sections and get perfect ribbons. 



In plant histology parafiin is used for cytologic work, and by many 

 whenever possible. Collodion must be used for the hard tissues and 

 is used by preference in some laboratories. (See references in the 

 collateral reading at the end.) 



Collodion sectioning is sometimes denominated the wet method, as 

 the tissue and sections must always be wet with some liquid, while 

 the paraffin ijiethod is called the dry method, as the tissue once in- 

 filtrated with paraffin keeps in the air indefinitely and in cutting 

 the sections no hquid is used. 



§ 625. Infiltration with ether alcohol. — Transfer the piece of tissue 

 to be cut from 95 % alcohol to a mixture of equal parts of sulphuric 

 ether and 95 % or absolute alcohol, and leave in this for a few hours 

 or a day or more, as is most convenient. This is to soak the tissue 

 full of a solvent of the collodion. 



§ 626. Infiltration with Ij % collodion. — Pour off the ether 

 alcohol from the tissue and add i§ % collodion. Leave in this over- 

 night or longer if the piece of tissue is large. 



