12 NORMAL HISTOLOGY. 



on the metal plate, and a spray of ether from an ordi- 

 nary two-bulbed atomizer being directed against the 

 lower side of the plate, the tissue will soon become 

 solid, and sections may be shaved off by placing the 

 knife held a little obliquely on the edge, like the knife 

 of a plane over the glass plate. These sections may 

 be studied unstained, or be stained with a one-per-cent. 

 aqueous solution of methyl green. This method is very 

 useful when it is desirable to determine the nature of a 

 tissue without waiting for the action of hardening 

 agents, as well as for seeing it in a nearly natural 

 condition. 



INJECTIONS. 



It is often desirable in studying the distribution 

 of the blood- or lymph-vessels to fill them by inj.ec- 

 tion with some colored substance by means of 

 which their ramifications may be readily recognized. 

 One of the most commonly employed injecting 

 materials is a solution of gelatin colored with 

 Prussian blue. This may be prepared as follows : 

 Dissolve 4 grms. of gelatin in 60 c. c. of water on a 

 water bath ; divide the solution into two portions ; 

 to one portion add 4 c. c. of a saturated solution of 

 ferrous sulphate (green vitriol), stirring constantly * ; 

 to the other add first 8 c. c. saturated solution of 

 potassium ferrocyanide, and then 8 c. c. saturated 



* Should the iron cause a pasty precipitate in the gelatin, this por- 

 tion should be allowed to cool, whe,n on warming again, with stirring, 

 it will dissolve. 



