554 
Vines . — • The Proteolytic 
cooling and filtering, the liquid is again heated and made 
alkaline with ammonia, and is then again saturated with 
ammonium sulphate. It is once more cooled and filtered, 
then boiled to drive off the ammonia, again saturated with 
ammonium sulphate whilst boiling, and made acid with acetic 
acid. The excess of ammonium sulphate is then got rid of 
by adding alcohol to the liquid ; most of the ammonium 
sulphate is precipitated, and the supernatant liquid holds 
in solution whatever peptone is present, which may be ulti- 
mately obtained by repeated treatment with alcohol and 
decantation of the supernatant liquid. 
With this method at my disposal, I had no difficulty in 
demonstrating the presence of peptone in the digestion-liquids, 
though it was necessary to concentrate these liquids before 
proceeding to test them. Mr. Ramsden also found peptone 
in a quantity of digestion-products precipitated by alcohol, 
which he was good enough to examine for me. 
I have nothing to add with regard to the other products 
of digestion, beyond the fact that I have been able to confirm 
my statement that leucin is one of them . 
Conclusion. 
1. The experiments relating to the action of high tem- 
peratures and of alkalies upon the enzyme confirm the 
statement made in my paper of last year with regard to its 
great stability; in fact, it would appear that it is the most 
stable of all known proteolytic enzymes. Whilst its activity 
can easily be much diminished by exposure to high tem- 
perature or treatment with an alkali, it still retains a sort of 
residual digestive power which asserts itself in very slow and 
prolonged digestion, and which can only be destroyed by 
relatively strong measures. 
2. It may, I think, be fairly concluded from the facts given 
in this paper, in conjunction with those which I published in 
1877, that the enzyme is derived from a zymogen present 
in the gland-cells. 
