190 PRACTICAL HISTOLOGY. 



may also be embedded in the same mixture, but in 

 such a way that the laminae, which in the matrix 

 represent the papillae of the skin, are cut transversely. 

 The sections must be as thin as possible, and stained 

 either with logwood alone or with picric acid and 

 logwood in the same way as was recommended for 

 the sections of skin, before being mounted in dam- 

 mar. 



But, owing to the substance of the nail being so 

 much harder than the subjacent matrix, it is very 

 difficult to get both parts equally thin. They can, 

 however, he got of much the same degree of hard- 

 ness by means of the gum method. The piece to be 

 cut, which should be quite small, is placed in syrupy 

 solution of gum and left over-night ; it is then 

 transferred to a mixture of spirit with one-sixth of 

 its volume of water. After a few hours the gum 

 which has penetrated into the substance of the tissue 

 will be hardened throughout, and the mass can be 

 embedded and cut in the desired direction, the knife 

 being wetted with some of the same spirit- mixture. 

 Strong spirit should not be used, since the gum is 

 entirely dehydrated by this, and becomes so hard as 

 to turn the edge of the knife. Instead of embed- 

 ding the piece in wax-mass it will be found a cleaner 

 and more convenient method to make a slit in a 

 winebottle cork, insert the hardened guru-impreg- 

 nated tissue in the proper position in the slit, and 

 maintain it in place whilst cutting the sections 

 by the pressure of the finger and thumb. The sec- 

 tions are transferred from the spirit to water, which 

 dissolves out the gum ; when quite free from this 

 they are stained and mounted as before. 



It will be well, before commencing the descrip- 

 tion of the mode of preparing the several viscera 

 for microscopical examination, to revert to one or 

 two preparations which were purposely deferred 



