GIACOMINI'S "DRY" PROCESS FOR PRESERVING BRAINS. 337 



time the ganglion-cells appear with their processes. Nuclei, vessels, and 

 whatever else may be in the preparation, are totally invisible. Merkel thinks 

 this method superior to all others for the study of the distribution of nerve- 

 fibres. The preparations are not permanent, though they may be kept for 

 some weeks by mounting them in Canada balsam. When a preparation 

 (either in xylol or balsam) has become so transparent as to be of no further 

 use (which will always eventually happen), it may be reprepared by 'putting 

 it back into the alcohol, and thence again into the xylol. 



BE VAN LEWIS (The Human Brain, p. 122) proceeds as follows : A sec- 

 tion is placed, saturated with spirit, on a slide. When the spirit has nearly 

 all evaporated, a drop of oil of anise is allowed to flow over the section (not 

 to float it up), and the clearing is watohed on the stage of the microscope ; 

 then, just when the desired image is arrived at, a drop of balsam is allowed 

 to run over the section, and a cover put on. 



Instead of oil of anise, Lewis has frequently employed glycerin followed 

 by mounting in glycerin jelly, with the same results. 



BYKOM BEAMWELL (Edinb. Med. Journ. Oct., 1886) also recommends 

 the process. He uses clove oil. 



678. GIACOMINI'S "Dry" Process for preserving Brains (Arch. per 

 le Scienze Mediche, 1878, p. 11). Although this is in intention a macro- 

 scopic method, it appears worth while, both on account of its thorough success 

 and on account of its suggestiveness, to give an account of it here. 



The object is to make " dry " preparations of the encephaloh ; by which 

 is meant preparations that can be permanently preserved in the air. The 

 methods hitherto employed were not successful because they consisted in 

 making preparations that were " dry " in the literal sense of the word, that 

 is, deprived cf their natural water ; and since brain-substance contains 88 per 

 cent, of water, such preparations could not of course be obtained without so 

 great an amount of shrinkage as to most seriously diminish the scientific 

 value of the result. The principle of Giacomini's method is, on the contrary, 

 to retain the natural water of the tissues, or an equivalent for it, by means 

 of impregnation with a hygroscopic substance, glycerin. 



The process consists of two divisions : 1, hardening ; 2, impregnation with 

 glycerin. 



1. For hardening may be used, zinc chloride, bichromate of potash, chromic 

 acid, nitric acid, or alcohol. 



Chloride of zinc gives the best results. Perfectly fresh brain is put into 

 a saturated aqueous solution of the salt (if there be reaspn to fear that the 

 tissues are somewhat -softened -through having been left too long after, the 

 (U-ath of the subject, it is well first to inject 600 grammes of the solution 

 through the internal carotid arteries). After forty-eight hours' immersion 

 (during which time the floating brain must be turned over three or four 

 times, so that all parts of it may duly come into contact with the liquid) the 

 surface of the brain will have attained a consistency that will allow of the 

 removal of the arachnoid and pia mater. The meninges having been removed, 

 the encephalon is put back into the solution for two or three days more, 

 during which time it will be seen that, increasing in specific gravity, it tends 

 towards the bottom of the vessel containing it. When this is seen to happen. 



22 



