72 THE CHEMICAL CONSTITUTION OF THE PROTEINS 



advisable to pour it into a fresh quantity of absolute alcohol. In this 

 way 200-300 grammes of silk peptone can be obtained. More can 

 be obtained by evaporating the alcoholic solution and repeating the 

 precipitation with alcohol. 



A purer product may be prepared if the original solution be 

 evaporated in vacuo as far as possible, dissolving the residue in hot 

 methyl alcohol and pouring into absolute alcohol. A still purer 

 preparation is obtained by precipitating a one per cent, solution with 

 I o per cent phosphotungstic acid solution, decomposing the precipitate 

 in the usual way and evaporating, etc. 



The preparation so obtained is easily soluble in water and has 

 generally an amphoteric or slightly acid reaction. 



The peptone is used in 10-50 per cent, solution, best 25 per cent. 

 If acid it is carefully treated with sodium bicarbonate till it is just 

 alkaline and filtered, if not clear. The enzyme solution is added and 

 the mixture is kept at 37 C. in presence of toluene. If a proteo- 

 clastic enzyme be present tyrosine separates out. Unfortunately the 

 method cannot be used quantitatively as some of the tyrosine is fre- 

 quently held back in the solution and is not easily separated on con- 

 centration. 



Numerous organs have been tested with this substrate ; proteoclastic 

 enzymes have been detected in the liver, kidney, muscle extracts, stomach 

 contents, faeces. Abderhalden and Heise tested for enzymes in the 

 various groups of invertebrates. All the animals tested contained 

 enzymes which hydrolysed the polypeptide. The parasitic intestinal 

 worms were proved to excrete no enzyme into the lumen of the intes- 

 tine, though the parasites contained active enzymes in their bodies. 

 Abderhalden and .Pringsheim have tested various moulds with the silk 

 peptone. They find with its use that in the method of Buchner for 

 preparing intracellular enzymes there is frequently adsorption of the 

 enzyme by the sand and " kieselguhr ". 



Abderhalden states that thin slices (one or several) of an organ 

 may be readily tested for proteoclastic enzymes ; they are placed in a 

 25 per cent, solution of the peptone, covered with toluene and kept at 

 37 C. in a closed vessel. Deposition of tyrosine appears on the sur- 

 face of the slice and sometimes after twelve hours there may be a con- 

 siderable amount of deposit This simple and convenient way of test- 

 ing for enzymes also serves for their localisation in cells and organs, e.g., 

 medulla and cortex of the kidneys. Using this method Abderhalden 

 has found that proteoclastic enzymes first appeared in seven to eight 



