164 PRACTICAL HISTOLOGY. 



the powdered carmine in the dry state. Even after 

 the production of this change a few more drops of 

 the acetic acid may be added, for it will do no harm, 

 and will tend to counteract the natural alkalinity of 

 the tissues. 



The colored gelatine is next filtered through a 

 piece of flannel or fine linen, previously soaked in 

 hot water, and again wrung out, and is collected in 

 a flask as it runs through the filter, and transferred 

 to the injecting bottle. 



For the blue injection 10 grammes of gelatine are 

 taken, and after having been soaked in cold water 

 and dissolved up as before, 50 c.c. of a 2 per cent, 

 solution of Berlin blue, which has been previously 

 warmed, is gradually added with constant agitation 

 to the fluid gelatine. The blue mixture is filtered 

 and is then ready for use, without the necessity of 

 precipitating the coloring matter, for ftiis being a 

 colloid is indiiFusible. 



It is sometimes advantageous in cases where the 

 structure of the walls of the bloodvessels is to be the 

 subject of observation, to use an injecting mass which 

 is far less deeply colored. This can of course be 

 readily obtained by diminishing the proportion of 

 carmine or Berlin blue which is used. 



The soluble Berlin blue is of great value for the 

 purpose of injecting both the bloodvessels and lym- 

 phatics. Unfortunately it is very troublesome to 

 prepare. The following is the method recommended' 

 by Briicke, to whom we owe its introduction : 



Take of potassic ferrocyanide 217 grammes, and 

 dissolve in a litre of water (solution A). 



Take a litre of a 10 per cent, solution of ferric 

 chloride (solution B). 



Take four litres of a saturated solution of sulphate 

 of soda (solution c). 



Add A and B each to two litres of c. Then with 

 constant stirring pour the ferric chloride mixture 

 into the ferrocyanide. Collect the precipitate upon 

 a flannel strainer, returning any blue fluid which at 



