283 



kidneys, &c., the juices of the tissues are apt to interfere 

 with the reaction, yet even here occasional success may be 

 attained. In practice it is often found advantageous to com- 

 bine the silver solution, intended for injection, with a certain 

 amount of gelatine, by which the blood-vessels are kept 

 handsomely distended, and the beauty of the preparation is 

 much increased. This plan was proposed by Chrzonszczewsky 

 in the paper already quoted. His formula, which I have 

 found to work well, is as follows : Half an ounce of fine 

 gelatine is dissolved in fotir ounces of distilled water, and to 

 this is added a solution of one scruple of nitrate of silver in 

 two fluid drachms of distilled water. After injecting with 

 this fluid, the tissue is exposed to the light precisely as after 

 the use of the simple silver solution. 



There are preserved in the Microscopical Section of the 

 Museum a number of silver stainings in which the epithelium 

 has been thus mapped out on the skin, the peritoneum, the 

 lymphatic-sacs of frogs, and the blood-vessels. These pre- 

 parations, after the action of the silver, have been mounted 

 in Canada balsam with or without the previous staining of 

 tlie nuclei Avith carmine. The detailed steps of the process 

 may prove useful to some readers. The silver staining having 

 been successfully accomplished, the nuclei are tinted prefer- 

 ably by the solution of carmine in borax, described by Thiersch 

 in his work on ej^ithelial cancer.^ It is prepared as follows : 

 Four parts of borax are dissolved in fifty-six parts of distilled 

 water and one part of carmine added to the solution ; one 

 volume of this fluid is mixed Avith two volumes of absolute 

 alcohol, and after crystals have formed the mixture is filtered. 

 The filtrate may be used for staining, but if the crystals of 

 carmine and borax which remain on the filter are dissolved 

 in a small quantity of distilled water, I find the solution thus 

 obtained answers a still better purpose. The portion of tissue 

 to be studied is soaked in this solution until coloured deep 

 red. It is afterwards treated with a saturated solution of 

 oxalic acid in alcohol, by which all colour is gradually 

 removed except from the nuclei. So soon as this is accom- 

 plished the piece is to be carefully washed in alcohol, then 

 soaked in absolute alcohol, and finally mounted in a solution 

 of dried Canada balsam in chloroform or benzole. The 

 treatment by oxalic acid, subsequently to the action of the 

 carmine-borax solution, has the additional effect of altering 

 the purplish-red colour, derived from that fiuid, to the 

 brilliant hue obtained by the use of the ammoniacal solution 

 of carmine ordinarily employed in histology. The latter has 

 I ' Der Epithelialkrebs.' Leipzic, 1865, S. 92. 



