131 
yeasts cause a slow liquefaction of wort gelatine; and Frankland,* in his 
description of S. liquefaciens, states that it liquefies gelatine fairly rapidly. 
This action of the three yeasts indicates the excretion of proteolytic 
enzymes. 
Though the statement relative to the extraction of a proteolytic 
enzyme from yeast is made of pressed yeast, no particular species being 
named, and there are various pressed yeasts, yet only in the three cases 
cited has the direct liquefaction of gelatine been noted. 
EXPERIMENTS. 
Among some wort gelatine yeast cultures I found one which had lique- 
fied the gelatine. On examining the culture it proved to be contaminated 
by another yeast from the air. The yeasts were separated, and when 
grown apart, the ‘‘wild’ yeast was found to be the one which caused the 
liquefaction. Cultures were made into both the ordinary beef broth gela- 
tine and wort gelatine’ to determine the constancy of this characteristic 
of the yeast. Tube and plate cultures of both kinds of gelatine showed 
liquefaction, the wort gelatine, however, being liquefied sooner than the 
beef gelatine. From thirty to forty days were required to liquefy a tube 
containing 6 cc. wort gelatine. The liquefaction was not uniform, even 
when conditions of media and temperature were alike. Wort gelatine 
plate cultures became liquefied in about two weeks. These results show 
undoubtedly the excretion of a proteolytic enzyme by the yeast. 
Investigations conducted by Fermi* have shown that antiseptics in 
small amounts are not injurious to enzymes. This property is taken ad- 
vantage of in the testing for enzymes, and also in determining, relatively, 
their strength. Water is saturated with thymol to which 5 per cent. of 
gelatine is added, then placed on a water bath until the gelatine is dis- 
solved, after which 10 cc. are placed in tubes. These are ready for use as 
soon as the gelatine sets.’ 
To test the strength of the enzyme produced by the yeast, I obtained 
extracts by filtering the liquefied gelatine from tube cultures. In the first 
experiment 3 cc. of the extract were used in each tube of thymol gelatine 
*Saceardo, P. A. Sylloge Fungorum, Vol. VIII, pp. 916-922. 
° Wort to which is added 7% gelatine. The wort had .23% acid, estimated as lactic. 
® Lafar, F. Technical Mycology, Vol. I, 1898, p. 300. 
7Same as ref. 6. 
