312 SUMMARY OF OUEEENT RESEARCHES RELATING TO 



altogether. Mix this with the glycerine, filter and place in a close- 

 stopped bottle. 



In this process nearly all the tannin is removed by percolating the 

 drug with cold water, a menstruum in which the colouring principle 

 is not very soluble, and the subsequent maceration and percolation 

 with the alum solution removes the logwood lake in a state of com- 

 parative purity. The glycerine is added simply for its preservative 

 qualities, and this may still be increased by the addition of a few 

 drachms of alcohol to the solution. 



The hematin staining fluid thus prepared is a clear heavy fluid of 

 a deep purplish red colour. It will keep its colour for a length of 

 time and deposits no sediment. A sample exhibited by the author 

 had been made for nearly a year, frequently exposed to a strong light 

 and open to the air, but was unchanged. Permanent and beautiful in 

 its colour, which is of a delicate violet hue, clear and sharp in its 

 definition of the different tissues under examination, it will bear use 

 with the very highest powers and it is hoped enables observers to 

 distinguish minute differences of tissue which have hitherto escaped 

 notice. 



As to the method of using the fluid, it yields good results when 

 used undiluted, as a quick stain ; but the best results are obtained by 

 placing the tissues in a weak solution (ten drops to two fluid drachms) 

 with warm distilled water for about twelve hours. This produces 

 results of surpassing delicacy and beauty. 



Dry Injection-masses* — The variously coloured gelatine emul- 

 sions in common use as injections keep for only a short time, and 

 have, therefore, to be prepared as occasion arises for their use. The 

 dry emulsions recommended by Dr. H. Fol are very easily prepared 

 and convenient in use. As they will keep for any length of time 

 they can be prepared in quantities, and will thus be ready for use at 

 any moment. 



Carmine Emulsion. — One kilogramme gelatine (softer kind used 

 in photography), soaked in water for a few hours until thoroughly 

 softened ; after turning off' the water, heat the gelatine over a water 

 bath until liquefied, and then add to it, little by little, one litre of a 

 strong solution of carmine in ammonia. The mixture, stiffened by 

 cooling, is cut up, and the pieces packed in a fine piece of netting, 

 Vigorous pressure with the hand under water forces the emulsion 

 through the net in the form of fine strings or vermicelli. These 

 strings are placed in a sieve and washed until they are free from acid 

 or excess of ammonia ; then collected and re-dissolved by heating. 

 The liquid is poured upon large sheets of parchment which have 

 been saturated with paraffin, and these sheets are then hung up to dry 

 in an airy place. The dried layers of the emulsion, which are easily 

 separated from the parchment, may be cut into strips and placed 

 where they are protected from dust and dampness. 



The carmine solution used in this emulsion is prepared as 



* Zeitschr. f. Wiss. Zool., xxxviii. (1883) pp. 492-5. Of. Amer. Natural., 

 xviii. (1884) pp. 219-20. 



