390 Pierre A. Fish 



note says : " From a note in Gratiolet (Memoire sur leplis 

 cerebraux del'homme. Paris. 1854, p. 11.) it is to be seen that 

 a Parisian modeller, Stahl, likewise used the zinc chlorid for 

 hardening brains, in order to make a cast of the same after- 

 ward, but it does not appear that Gratiolet employed the same 

 process in his anatomical researches. " Bischoff himself had 

 used it for some years previous to 1868. 



It is a deliquescent salt and specimens should not be left too 

 long in its solution lest they soften. The hardening is con- 

 tinued in alcohol. Aqueous solutions are generallj' used since 

 enough of the salt may be dissolved to support the brain. 

 Broca' (1879), was perhaps the first to recommend it in an al- 

 coholic solution (ten per cent.). It acts here as a very strong 

 dehydrant, but its action is even if rapid, and with careful 

 treatment no marked distortion results. It has also proven 

 ^ eminently satisfactory for histological work, but for this a five 

 per cent, solution is apparently just as efficacious as the strong- 

 er. The specific gravity of a saturated alcoholic solution is 

 not great enough to buoy the brain, and a bed of cotton is 

 therefore necessary. 



Glycerin makes a very efficient preservative. It is, however, 

 generally utilized as an adjunct in methods more or less com- 

 plex or for the immersion of specimens that have already been 

 hardened. 



Nitric acid in a ten or twelve per cent, solution has also 

 been recommended ; the specimen is to be immersed from 

 twelve to fifteen days and turned frequently as the liquid is too 

 dense to admit of its being entirely covered. This reagent is 

 said to give the toughest of preparations. 



Experiments were made in May, 1892, to determine ap- 

 proximately the relative loss of weight and girth of a number 

 of sheep brains prepared in different ways. The girth was 

 ascertained by measuring transverselj' around the brain at 

 the level of the temporal lobes. This as well as the weight 

 was determined at three stages during the course of hardening : 

 first, when fresh ; second, the intermediate stage, or before 

 the specimen was brought into alcohol ; third, after immersion 

 in alcohol for a longer or shorter time. The accompanying 

 table shows ver}' concisely the results thus obtained. 



