210 PRACTICAL HISTOLOGY. 



appearance of the aveoli in the charged and discharged 

 conditions respectively of the glands are noted. 



Preparation 12. Most of the ordinary hardening 

 solutions (alcohol and chromic acid, for instance) con- 

 siderably alter the salivary cells, so that in sections of 

 the glands the cells are scarcely ever seen of their normal 

 form and appearance. Osmic acid preserves them in a 

 more natural condition than most reagents, so that, to 

 study the individual elements, a very small portion may 

 be placed in a 1 per cent, solution of this reagent, and 

 after forty-eight hours broken up finely in a drop of 

 water on a slide. The preparation may be preserved in 

 glycerine. 



