INJECTION GELATIN MASSES. 301 



tories, and also because it often happens that commercial 

 gelatin is acid. 



The mass having been perfectly neutralised is strained 

 through new flannel. 



484. How to Neutralise a Carmine Mass (YiLLE,, Gaz. hebd. d. 

 Sci. mrd. de Montpellier, Fev., 1882; may be had separately 

 from Delahaye et Lecrosnier, Paris) . VILLE points out that 

 when carmine is treated with ammonia a certain proportion of 

 the ammonia combines with the carmine to form a trans- 

 parent purple compound, and the rest remains in excess. It 

 is this excess that it is required to neutralise precisely, not 

 the u-ltole of the ammonia employed. 



As to the acidity accidentally found in commercial gelatin, 

 that source of error is easily eliminated. Instead of soaking 

 the gelatin in water, it should be placed in a large funnel 

 with a narrow neck, or better, in a stopcock funnel, and the 

 whole should be placed under a tap, and a stream of water 

 arranged in such a manner that the gelatin be constantly 

 completely immersed. Washing for an hour or so in this 

 way will remove all traces of acids mechanically retained in 

 the gelatin. 



As to the neutralisation of the colouring mass, VJLKK is of 

 opinion that the sour smell cannot be safely relied on in 

 practice. He considers it greatly preferable to employ 

 exceedingly delicate dichroic litmus paper (litmus paper 

 sensitised so as to be capable of being used equally for the 

 demonstration of acids and bases) . Such paper is, I believe, 

 now found in commerce ; for directions for preparing it and 

 for preserving ammonia without loss of strength, and other 

 details, see previous editions. 



485. HOYKR'S Carmine-Gelatin Mass (Biol. Centralb., 1882, 

 p. 21). Take a concentrated gelatin solution and add to it 

 the needful quantity of neutral carmine staining solution (he. 

 cit., p. 17). Digest in a water-bath until the dark violet-red 

 colour begins to pass into a bright red tint. Then add 5 10 

 per cent, by volumes of glycerin, and at least 2 per cent, by 

 weight of chloral, in a concentrated solution. After passing 

 through flannel it can be kept in an open vessel under a bell- 

 glass. 



