THE PRACTICE OF HARDENING. 45 



CHAPTER VI. 



HARDENING EEAGENTS. 



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. But there are some 

 exceptions. Such are, for instance, the cases in which it is 

 desired to cut very large sections, such as sections 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- And certain organs 

 that are either extremely delicate or inaccessible, such as 

 retina or cochlea, will require to be specially hardened in 

 order to give the best results. 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 

 will soon become seriously altered by the diffusion into it of 

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



