IMBEDDING- METHODS 495 



important not to confound it with basic fuchsin, ;is appears to 

 liave been done by some writers. For staining- sections a \ per 

 cent, solution in water may be employed, and allowed to act oil 

 sections for from one to five minutes. A red stain, very resistent to 

 alcohol and acids, and permanent in balsam. It is an excellent stain 

 for use after a blue nuclear stain, such as hsematoxylin, thionin, 

 gentian violet, or the like. 



The celebrated mixture known as the Ehrlich-Biondi-Heidenhain 

 stain involves such complicated and delicate manipulations as to be 

 totally unsuitable for ordinary histological work. 



Imbedding Methods, 'The beautiful processes known as 

 imbedding methods are employed for a threefold end. Firstly, they 

 enable us to surround an object, too small or too delicate to be 

 firmly held by the fingers or by any instrument, with some plastic- 

 substance that will support it on all sides with firmness but without 

 injurious pressure, so that by cutting sections through the 

 composite body thus formed, the included object may be cut into 

 sufficiently thin slices without distortion. Secondly, they enable us 

 to fill out with the imbedding mass the natural cavities of the object, 

 so that their lining membranes or other structures contained in 

 them may be duly cut in situ. And. thirdly, they enable us not 

 only to surround with the supporting mass each individual organ or 

 part of any organ that may be present in the interior of the object, 

 but also to impregnate with it each separate cell or other anatomical 

 element, thus giving to the tissues a consistency they could not other- 

 \\ ise possess, and ensuring that in the thin slices cut from the mass 

 all the details of structure will precisely retain their natural relations 

 of position.' 



' These ends are usually attained in one of two ways. Either the 

 object to be imbedded is saturated by soaking with some material 

 that is liquid while warm and solid when cold, which is the principle 

 of the paraffin process ; or the object is saturated with some 

 substance which whilst in solution is sufficiently fluid to penetrate 

 the object to be imbedded, whilst at the same time, after the 

 evaporation or removal by other means of its solvent, it acquires and 

 imparts to the imbedded object sufficient firmness for the purpose 

 of cutting,' which is the principle of the celloidin process. (From 

 Mr. Lee's ' Microtomist's Vade-mecum.') 



Any substance used for imbedding is technically termed an 



'imbedding mass.' 



The older workers were not aware of the importance of 

 thoroughly saturating the objects to be cut with the imbedding 

 mass, a point which is very important in order to the production 

 of thin and undistorted sections. They were content with simply 

 surroundiny the objects to be cut with the mass. This primitive 

 procedure is now rightly abandoned, except in cases in which, on 

 account of the large size or other peculiarities of the object, it is 

 impossible to procure due saturation. 



Among the numerous methods of imbedding that have been 

 advocated, only two are in general use at the present day. These 

 are the paraffin method, and the collodion or celloidin -itu't/tod. And 



