THE PEEPAEATION OF ANIMAL TISSUES. 39 



In hardening tissues it is all important to secure 

 that the specimens shall be thoroughly penetrated 

 by the liquid in which they are placed, and to this 

 end it is necessary to immerse them in an abund- 

 ance of the liquid say into 100 times their bulk, 

 or even more and to divide them into sufficiently 

 small pieces to ensure this result, regard, of course, 

 being had to the attainment of sections of sufficient 

 size to show the structure and features of the 

 various organs this latter consideration, in these 

 days of large sections, being obviously a matter of 

 the greatest importance. 



The tissues must be as fresh as possible. Parts 

 which have to be treated by the gold or silver 

 processes must be immersed within half an hour 

 after death, or they will cease to be susceptible to 

 the action of re-agents. The time of year also must 

 be a matter of consideration, summer and hot 

 weather being, of course, less favourable to the pre- 

 servation of animal matter than the cold of winter. 

 No tissue can be placed too early in the preservative 

 medium ; all useless matter, such as the contents of 

 the stomach or intestines, must be carefully washed 

 away with f per cent, salt solution. As soon as 

 a fluid has become " fouled " by the tissues placed 

 in it, it should be changed ; as a rule, frequent 

 changes are advisable. 



All tissues hardening in chromic acid solutions 

 must be examined daily, after the first few days, 

 to prevent them from becoming brittle and thus 

 spoiled. Different tissues placed in the same 

 medium should be separately examined and tested. 

 Some may have become sufficiently hardened and 

 require immediate removal, whilst a more prolonged 



