30 CHAPTER III. 



that a certain, slight proportion of colloids in the hardening 

 liquid is favourable to the desired reaction, as it gives a 

 better consistency to the tissues by preventing them from 

 becoming brittle. Hence the utility of employing a certain 

 proportion of hardening agent. 



Hardening had better be done in tall cylindrical vessels, 

 the objects being suspended by a thread, or muslin bag, or 

 otherwise, at the top of the liquid. This has the advantage 

 of allowing diffusion to take place as freely as possible, 

 whilst any precipitates that may form fall harmlessly to the 

 bottom. 



In general begin hardening with a weak reagent, increasing 

 the strength gradually, as fast as the tissues acquire a consist- 

 ence that enables them to support a more energetic action 

 of the reagent. 



Let the objects be removed from the hardening fluid a 

 soon as they have acquired the desired consistency. 



