THE PRACTICE OF HARDENING. 43 



01 



S 



CHAPTER VI. 



HARDENING AGENTS. 



67. The Obligation of Hardening. Methods of imbedding 

 have now been brought to such a degree of perfection that 

 the thorough hardening of soft tissues that was formerly neces- 

 sary in order to cut thin sections from them is now, in the 

 majority of cases, no longer necessary ; by careful infiltration 

 with paraffin or some other good infiltration mass, most soft 

 objects can be satisfactorily cut with no greater an amount of 

 previous hardening than is furnished by the usual passing of 

 the tissues after fixing through successive alcohols in order to 

 prepare them for the paraffin-bath. Almost the only excep- 

 tions to this statements are, I believe, to be found in the cases 

 in which it is desired to cut very large sections, such as sec- 

 tions of the entire human brain. Such an organ as this cannot 

 be duly infiltrated with alcohol in a few hours, and it is 

 doubtful whether it can be duly infiltrated with paraffin or any 

 other imbedding mass in any reasonable time. The processes 

 employed for hardening such specimens as these will be 

 described when treating of the organs in question; in this 

 chapter, which may be considered as parenthetical, I confine 

 myself to such general statements concerning the employment 

 of the usual hardening agents as appear likely to be generally 

 useful. 



68. The Practice of Hardening Hints and Cautions. Employ 

 in general a relatively large volume of hardening liquid, and 

 change it very frequently. The exact proportions .may be 

 made out by experiment for each reagent and each class of 

 objects. If the volume of liquid be insufficient, its composition 



ill soon become seriously altered by the diffusion into it of 

 he soluble substances of the tissues ; and the result may be 

 a macerating instead of a hardening liquid. Further, as soon 



