292 
Vines . — The Proteases of Plants . 
Yeast (Saccharomyces Cerevisiae). 
In a previous paper (6) I expressed the opinion, as the result of a few 
experiments, that yeast contains a proteolytic enzyme which is active 
in neutral and in acid liquids but not in alkaline. At that time I had not 
seen the paper in which Hahn and Geret ( 7 ) have given a full account 
of their very thorough investigation of this subject : their results are of 
such interest that a brief re'suml of them will not be out of place. They 
worked with the expressed juice of fresh yeast, a liquid that contains 
a considerable amount of proteid coagulable on boiling, and is also spon- 
taneously coagulable on being kept in the incubator at 37°C. for two hours. 
They ascertained that this liquid digested fibrin within twenty-four hours ; 
but their investigation was directed more especially to the self-digestion 
(autolysis) of the liquid. Their method of estimating digestive activity 
was the comparison of the weights of the coagulum obtained from a given 
quantity of juice before and after digestion. For instance, in one case 
the weight of coagulum obtained before digestion was taken as 100, the 
weight after autolysis for twenty hours was 9*1. By this means they 
ascertained (a) that the natural acid juice digests actively ; ( b ) that its 
activity is diminished, though not to any great extent, by such antiseptics 
as chloroform, thymol, toluol, salicylic acid, and hydrocyanic acid (HCN) ; 
(c) that it is increased by the presence of neutral salts, such as NaCl 3 °/ o , 
KN 0 3 i°/ 0 , KN 0 3 io°/ o ; (d) that it is increased by the addition of HC 1 
from 0*05 °/ o up to 0-3 °/ o , o-2°/ o HC1 being the optimum, and that it is 
diminished in the presence of o*5°/ o HC 1 , and almost destroyed by HC 1 i°/ o ; 
(e) that the activity is diminished by neutralization, and still more so 
by alkalinity of o-2-o*5 °/ o NaHO. The inferences that they draw as to the 
nature of the proteolytic enzyme will be discussed in the concluding section 
of this paper. 
Since the publication of the paper by Hahn and Geret, the only other 
contribution to the study of yeast-proteolysis is, so far as I am aware, 
that of Bokorny (8). He investigated the action of dried yeast, used in the 
solid form, upon various proteids either of animal or of vegetable origin : 
his experiments were made exclusively with liquids containing from 0-2-2 °/ o 
of added acid, chiefly phosphoric, without, apparently, any antiseptic, their 
duration varying from three hours to three days. The measure of digestive 
activity was the amount of the precipitate obtained on treating the concen- 
trated digestion-liquid with excess of alcohol : the nature and relative 
quantity of the products was determined by dissolving the alcohol-precipi- 
tate in water, when any albumose present could be precipitated by saturation 
with ammonia sulphate or zinc sulphate, and any peptone by precipitation 
with phosphotungstic acid from the filtrate obtained after the separation 
of the albumoses. 
