298 CHAPTER XXII. 



these cases it may be advisable to use nitrite of amyl as a 

 vaso-dilator. The animal may be anaesthetised with a mix- 

 ture of ether and nitrite of amyl, and finally killed with 

 pure nitrite. Or, after killing by nitrite, a little nitrite of 

 amyl in salt solution may be injected before the injection 

 mass is thrown in. In any case it is advisable to add a 

 little nitrite to the mass just before using. The relaxing 

 power is very great (see OVIATT and SARGENT, in St. Louis 

 Med. Journ., 1886, p. 207 ; and Journ. Roy. Mic. Soc., 1887, 

 p. 341). 



477. Foi/s Metagelatin Vehicle (Lehrb., p. 17). The opera- 

 tion of injecting with the ordinary gelatin masses is greatly 

 complicated by the necessity of injecting them warm. FOL 

 proposes to employ metagelatin instead of gelatin. 



If a slight proportion of ammonia be added to a solution 

 of gelatin, and the solution be heated for several hours, the 

 solution passes into the state of metagelatin, that is-, a state 

 in which it no longer coagulates on cooling. Colouring 

 masses may be added to this vehicle, which may also be 

 thinned by the addition of weak alcohol. After injection, 

 the preparations are thrown into strong alcohol or chromic 

 acid, which sets the mass. 



KOBIN'S Masses. 



478. ROBIN'S Gelatin Vehicle (Traite, p. 30). Take some 

 good gelatin, soak it in cold water, then heat in water over 

 a water-bath. One part of gelatin should be taken for 

 every 7, 8, 9, or even 10 parts of water ; it is a common 

 error to employ solutions containing too much gelatin. The 

 solution is now to be combined with one of the colouring 

 masses given below. 



This vehicle, like all gelatin masses, is liable to be attacked 

 by mould if kept long ; camphor and carbolic acid do not 

 suffice to preserve it. 



Chloral hydrate added to the mass is said to preserve it 

 (HOYER). A sufficient dose, at least 2 per cent., should be 

 employed (see below, 485). 



