Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/230

 then it is similarly freed from water, as far as possible, before being placed in sulphuric acid, which is kept cool by means of ice. Nervous tissue, after it has been deprived of all blood and boiled, must first be extracted with carbon tetachloride, as otherwise its lipoidal sheath makes decomposition very difficult. Tubercle bacilli must also be freed from lipoids.

For hydrolysis, we use 70 per cent. (by weight) of sulphuric acid, which must be cold. We take three times as much of this, as of the tissue to be decomposed. The vessel is energetically shaken, and then carefully stoppered. From time to time it is shaken again. The tissue is soon dissolved, the solution becoming more or less brown. After standing for exactly three days, at the temperature of the room (20° C. at most), the vessel containing the hydrolysate is placed into iced water, and diluted with ten times its quantity of distilled water. The addition must be made very gradually. The temperature of the solution is controlled by means of a thermometer, and must never be allowed to rise above 20° C. If the vessel is too small, then the solution is transferred into a larger one, and the water with which we are diluting is used to rinse the first vessel.

We now begin the neutralization of the sulphuric acid with barium hydroxide. Pure crystalline hydroxide is employed for this purpose, and this is gradually added, until the solution gives no