WITH THE MICROSCOPE. 303 



fifth. The process of flattening may be pushed still further if 

 desirable, and if only carried out very slowly by gentle taps or 

 careful pressure with the finger and thumb, from day to day, the 

 elements of the tissues are gradually separated without being 

 destroyed. If there be much connective tissue, which interferes 

 with a clear view of the finest nerve or muscular fibres, it may be 

 necessary to immerse the specimen for some days in the acetic acid 

 syrup, and then transfer it to fresh glycerine. 



The success of this process depends upon the care and patience 

 with which it is carried out. The most perfect results are obtained 

 in cases where the washing, pressure, and warming have been very 

 slowly conducted, and it is most interesting to notice the minute 

 points of structure which are gradually developed and rendered 

 clearer by the repeated application of a gentle heat, subjecting the 

 specimen to a little firmer pressure or by furtherjsoaking in a little 

 fresh glycerine placed in a watch-glass. 



Specimens of tissue prepared in this way can be transferred from 

 slide to slide, and no matter how thin they may be, after having 

 been allowed to soak in fresh glycerine they may always be laid out 

 again perfectly flat by the aid of needles upon another slide. 

 The action of these viscid fluids is most valuable, and I feel sure 

 that by the process here given, the principle being retained but 

 the details modified in special cases, many new and important 

 anatomical facts will be discovered. 



The process of preparing the papilla? of the frog's tongue is 

 precisely the same. Small pieces of the mucous membrane being 

 removed by sharp scissars, they are transferred to glycerine, subjected 

 to the same very gradually increased pressure, until the individual 

 papillae are themselves slightly flattened. It is possible from a spe- 

 cimen to remove a number of the separate papillae on a needle point, 

 transfer them to glycerine or to the acetic acid syrup, and then mount 

 them for examination with the -^th object-glass All the points I 

 have described and figured in my paper (Royal Society, 1864) may 

 then be demonstrated in several papillae, pi. LXIII, fig. 389. 



Thin sections of brain, spinal cord, &c., may be subjected to the 

 same process for examination with the highest powers. The speci- 

 mens illustrating my paper on ' Indications of the paths taken by 

 the nerve currents as they traverse the caudate nerve cells of the 

 spinal cord and encephalon,' published in the Proceedings of the 

 Royal Society, July, 1864, were prepared in the manner already 

 described, but they were soaked for some months in a weak glycerine 

 solution of acetic acid. The most delicate preparations retain their 

 characters for many months, and some for several years, so that in 



