— 139— 



It will also be noticed that the mass changes its color, l)e- 

 coming a brigliter red. If the mass becomes too iitid it 

 appears granular if a drop is examined under the micro- 

 scope; in this state it is not entirely useless, but the result- 

 ing injection is never so good as when the mass is neutral. 

 Before using, the mass must be strained through a 

 piece of flannel which has been dipped in hot water. 'J'he 

 canula, syringe, and animnl must be kept warm during the 

 injection. If the entire animal is to be injected, the canula 

 is to be tied into the arch of the aorta, through the left 

 ventricle ; if a single organ, the canula is tied into its main 

 artery. As soon as the injection mass appears in the 

 accomi)anying vein, this vein is firmly tied. After the 

 tissues- havf l)een fully iujecteil, the animal or organ is set 

 aside in a cold place until the injcftion congeals, the tissues 

 are then removed, cut into small pieces, and hardened in 

 alcohol. These may, before embedding, be stained in 

 Del afi( 'Id's b Hematoxylin. 



Berlin Blue Mass (Harting, as given l)y Rawitz). 



One part of oxalic acid is " rubl)ed up " in a glass 

 mortar; to this is added one part of Berlin blue, and, while 

 constantly stirring, 12 parts of water. To an equal quantity 

 of warm gelatin solution (made as above directed) add the 

 Berlin ])lue solution slowly, continually stirring. Filter 

 through a })iece of flannel before using. 



Inject while the solution is warm. After the tissues 

 are cold, harden in alcohol. The tissues may l)e stained in 

 alum or Ijorax carmine. 



