THE KIDNEY. 217 



the most satisfactory results. To insure this desirable end, it 

 is necessary that the sulphindigate of soda be pure. 



O. Maschke, of Breslau, the apothecary who manufactures the pure sulphin- 

 digate of soda for Prof. Heidenhain, writes to that author as follows : " The 

 indigo- sulphate of soda was prepared from the phcenicin-sulphate of soda. If 

 the latter compound be heated for half to one hour, at a temperature of 60 to 

 70 C., with five or six times its volume of sulphuric acid of a specific gravity 

 of 1,840, it resolves itself completely into indigo- disulphate of soda and 

 indigo-monosulphate of soda (indigunterschwefelsaures Natron). I have 

 chosen this mode of preparing the salt because the indigo-gelatine and indigo- 

 brown can easily be separated from the phoenicin-sulphate of soda, without 

 marked loss, and in this way I obtain a sufficiently pure substance for future 

 use. An easier method of preparing the salt is the formula given by Crum 

 and Berzelius. One part of best indigo in powder is gradually added to seven 

 or eight parts of pure sulphuric acid, specific gravity 1,840, in a large vessel, 

 and the two thoroughly mixed. After the liquid has ceased to froth, the 

 vessel is covered with an animal membrane and put aside for three days, during 

 which interval it is to be frequently shaken. To this solution thirty to forty 

 volumes of water are added, and the whole carefully filtered. To the resulting 

 clear solution as many parts by weight of crystallized carbonate of soda as 

 there were of sulphuric acid, are added. Owing to the effervescence which 

 now takes place, the vessel in which the mixture is prepared must be of large 

 size. For this reason it is better to substitute the acetate of soda, or chloride 

 of sodium, or simply sulphate of soda, for the formation and precipitation of 

 the indigo-disulphate of soda takes place with any soda salt which does not 

 decompose the indigo -disulphuric acid. The mixture is now filtered, and the 

 precipitate dried over a water-bath. It is then pulverized and treated re- 

 peatedly with absolute alcohol, which dissolves any indigo-monosulphate of 

 soda, acetate of soda, or indigo-red, which may have remained." In this way 

 the indigo-carmine is obtained in a pure state. The crystals are copper-colored, 

 but the salt is blue in the pulverized state. The indigo-carmine of commerce 

 is an impure article and cannot be used for natural injection. 



For injection, a cold saturated solution of the sulphindigate 

 of soda is used ; the salt may be dissolved in boiling distilled 

 water, and the solution allowed to cool. A dog or rabbit 

 answers for the purpose of injecting. The animal is properly 

 fastened to a board, and the external or internal jugular vein 

 dissected up and exposed. In either of these vessels a canula 

 with stop-cock, previously filled with the indigo- carmine 

 solution, is inserted. The injection into the jugular may be 

 made downward or upward the latter is preferable. A syr- 

 inge, graduated in cubic centimetres and containing the sol- 

 ution of indigo-carmine, is now attached to the canula, the 

 stop-cock opened and a small quantity of the solution injected 



