38 PKACTICAL HISTOLOGY. 



tion upon the protoplasmic white corpuscles as well 

 as upon the very easily alterable red disks, and this 

 fact must be borne in mind in investigating the ac- 

 tion of reagents or poisonous substances, both upon 

 the blood-corpuscles and upon the tissues generally. 

 If a reagent is to be employed in weak solution, 

 therefore, it is well to dissolve it either in salt solu- 

 tion or in fresh serum 1 instead of water. Washing 

 with water tissues which are subsequently to be sub- 

 mitted to microscopical examination, as is so freely 

 done in the post-mortem room, is for a similar rea- 

 son to be deprecated ; but if a trace of bichromate of 

 potash or of chromic acid, or a little common salt be 

 previously added to the water, its deleterious effect 

 upon the protoplasm is in great measure obviated. 



Preparation 4. Action of Acetic Acid. To 

 investigate the action of dilute acids, it is best, as 

 just explained, to mix the acid with salt solution 

 instead of water ; 1 part of glacial acetic acid to 200 

 of salt solution is an appropriate strength for the 

 blood. The preparation is made in the usual way, 

 and the drop allowed to run in at the edge of the 

 cover-glass. The action of the weak acid upon the 

 red corpuscles is seen to be quite like that of water; 

 they are first rendered globular and then decolor- 

 ized. Upon the white corpuscles it has a somewhat 

 different action, for although the protoplasm of the 

 corpuscle becomes partly swollen out into a clear 

 spheroid, the nuclei are not swollen by the reagent, 

 but are brought very distinctly into view, as well as 

 the nucleoli within them, and remain usually at one 

 side of the corpuscle, with a little granular matter 

 precipitated around them. 



Preparation 5. Action of Tannic Acid. The 

 action of tannic acid upon the red corpuscles is pe- 

 culiar and interesting. Like other acids it tends to 

 cause the colored part of the red corpuscle to become 



1 The scrum employed must be from the blood either of the 

 same animal or ot'uue belonging to the same species. 



