139 



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

 coming a brighter red. If the mass becomes too acid 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. The 

 canula, syringe, and animal 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 

 accompanying vein, this vein is firmly tied. After the 

 tissues have been fully injected, the animal or organ is set 

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

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

 alcohol. These may, before embedding, be stained in 

 Delafield's hsematoxylin. 



Berlin Blue Mass (Harting, as given by Rawitz) . 



One part of oxalic acid is " rubbed 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 blue solution slowly, continually stirring. Filter 

 through a piece of flannel before using. 



Inject while the solution is warm. After the tissues 

 are cold, harden in alcohol. The tissues may be stained in 

 alum or borax carmine. 



