64 



THE MICROSCOPIST. 



ment," which are the products of its activity. Carmine, 

 anilin, haematoxylin, and picric acid, are used for staining 

 by imparting their own color to tissues ; while nitrate of 

 silver, chloride of gold, chloride of palladium, and peros- 

 mic acid stain, by their chemical action, often under the 

 reducing influence of light. (See Fluid Media.} 



Injecting Tissues. Injections of the vessels in animal 

 tissues are resorted to either to exhibit their course or the 

 structure of the vascular walls. For the latter purpose a 

 solution of nitrate of silver is commonly employed, for the 

 former either opaque or transparent coloring matter. (See 

 Fluid Media.} 



The injecting syringe (Fig. 35) is made of brass or Ger- 



FIG. 35. 



Injecting Syringe. 



man silver. One of the pipes should be inserted into the 

 principal vessel, as the aorta of a small animal, the um- 

 bilical vein of a foetus, or the artery, etc , of an organ, 

 and should be securely fastened by a thread. All other 

 open vessels should be tied. The solution of gelatin, or 

 other matter used, should be strained, so as to be free 

 from foreign particles, and should be forced into the ves- 

 sels with a gentle, steady pressure on the syringe. 



Injections should be made soon after the death of the 

 animal, or else after the rigor mortis has subsided. 



