HARDENING BT THE FREEZING METHOD. 317 



CHAPTER XXX. 



CENTRAL NERVOUS SYSTEM. 



657. Introductory. For small objects, such as the spinal cord and en- 

 cephalon of very small Mammalia and of inferior Vertebrata, the ordinary 

 methods of microscopic anatomy are very often sufficient. The cord and 

 encephalon of Batrachia, for instance, may be treated as follows : Corrosive 

 sublimate, half an hour or so ; alcohol of from 50 to 70 per cent., about two 

 hours ; then borax-carmine, or Mayer's alcoholic cochineal ; paraffin ; and 

 sections mounted in balsam. The same organs of somewhat larger animals, 

 such as the cat or rabbit, can also be prepared without recourse to any very 

 special methods. They may be fixed and hardened in liquid of Erlicki, or 

 other bichromate solution, well washed out with water, stained and imbedded, 

 or first imbedded in collodion and stained after sectioning with alum-carmine, 

 ammonia-carmine, or Heidenhain's hsematoxylin, or, if it be desired to study 

 the topography of nerve-fibres, with Weigert's ha3inatoxylin. Even the 

 cord of Man may be treated by these methods ; or rather, could be so treated if 

 it did not almost always come into the hands of the anatomist in a state of post- 

 mortem softening that necessitates special precautions in the hardening process. 



But the voluminous encephala of Man and the larger Vertebrates cannot 

 be thus simply treated. They require specially modified methods for har- 

 dening, for the manipulation of sections, and for staining. 



These methods have lately been described with great completeness in the 

 works of BE VAN LEWIS (The Human Brain ; Histological and Coarse 

 Methods of Research, London (Churchill) ; and OBERSTEINER (Anleitung 

 beim Studium des Baues d. nervosen Centralorgane im gesunden u. Jcranken 

 Ziixftt il<', Leipzig (Toeplitz). These very welcome additions to the literature 

 of the subject relieve me from the obligation of treating the subject with all 

 the minuteness that might be desired by specialists ; the more so, as they 

 show that so to treat the subject requires a volume, not a chapter. 



Hardening. 



658. Hardening by the Freezing Method. This is in many cases 

 a very good method, and in particular may be of service for the histological 

 study of the cortex. 



If it be desired to freeze an organ that has been already hardened by re- 

 agents, the five/ing may be done by means of a freezing mixture of ice and 

 salt; but in this case the preparation should first be penetrated by a muci- 



