256 E. T. NEWTON ON THE PREPARATION OF SOFT TISSUES. 



Attention was called to the method of imbedding objects so that 

 they may be more firmly held when sections are to be cut, and the 

 various mixtures of white wax and oil, paraffin-wax, and lard, &c., 

 were mentioned. The degree of hardness of the imbedding sub- 

 stance was stated to be of some importance, particularly when a 

 machine is used, for if the wax be too hard the edge of the razor 

 (which must always be very thin for delicate work) will have a ten- 

 dency to glide over the top instead of cutting into the wax. 



It is sometimes found convenient to imbed objects in gum, and to 

 do this the tissue should be soaked in a thick solution of gum 

 arable, and then placed in a paper tray with some of the gum 

 solution ; the tray is then allowed to stand in a vessel containing 

 spirits of wine until the gum becomes hard enough to be cut with a 

 razor. 



Some objects may be placed between pieces of fresh carrot and 

 then cut ; and in those cases where it is is applicable, this is an 

 admirable material for the purpose, as it cuts very easily, and is at 

 the same time firm and tough. 



When speaking of the " cutting instruments" used for prepar- 

 ing sections, the author gave it as his opinion, that although ordi- 

 nary razors answered very well when sections were being cut by 

 hand, yet when one of those machines was used in which the knife 

 has to move upon a flat plate, the ordinary form of razor did not 

 answer, for it was found that the curved edge had a tendency to cut 

 the edges of the aperture in which the object was held, and in this 

 way the cutting edge was spoiled. The form of knife advocated 

 was one which had the cutting edge quite straight and parallel with 

 the back, the latter being thick ; both sides of the knife should be 

 hollowed. The length and width of the blade should be in some 

 measure proportionate to the size of the section to be cut. What- 

 ever the form of the knife, it is absolutely necessary for the pre- 

 paration of thin sections of soft tissues that its cutting edge be 

 very sharp and thin 



With regard to the staining of preparations, Beale's Carmine 

 Solution was mentioned as being most generally useful for ordinary 

 tissues. Nerve tissues require longer immersion in the staining 

 fluid, and very good results were said to have been obtained by 

 using a strong ammoniacal solution of carmine. (See " Quart. 

 Micro. Journal," 1872, p. 10). It sometimes happens, more espe- 

 cially with sections of nerve tissues, that in the process of washing 



