1899 - 1900 .] Dr J. S. M‘Kendrick on Enzymes in Tissues. 87 
sputum has a marked inversive action. It has a faint power in 
the conversion of starch into sugar (probably from ptyalin in 
saliva), and in the digestion of fibrin in an acid medium. Both 
these reactions are slight, as compared with the inversive power. 
As I have mentioned before, the result is probably due to the 
liberation of an organised ferment from the pyogenic or other 
organisms which exist in sputum after their death. 
IX. Extracts op Malignant Tumours. 
The few carcinomata and sarcomata that were examined yielded 
extracts which converted starch into sugar, and also which digested 
fibrin slightly in an acid medium. 
Do THE ABOVE RESULTS DEPEND THEN ON THE ACTIVITY OP 
Enzymes 1 
This problem naturally presents itself, hut I fail to see how any 
other explanation would account for the results. The glycerine 
extract itself has no reaction on starch or fibrin unless heated to 
the proper temperature, and kept at this temperature for a suffi- 
cient length of time. The extract must he treated in exactly the 
same manner as a solution containing a pure enzyme. In all 
respects there is proof that when a reaction occurred it depended 
upon enzymic activity. When starch was converted into sugar, 
this depended upon the enzyme ptyalin or amylopsin, or a similar 
enzyme. When fibrin was dissolved, and peptones were formed in 
an acid solution, then the enzyme pepsin was at work : or, again, 
when fibrin was dissolved, and peptones were formed in an alkaline 
solution, then trypsin was in action. When cane sugar was 
inverted into dextrose, this depended upon the enzyme inversin 
or a similar enzyme ; and lastly, when the milk curdled, an enzyme 
similar in its action with rennin was at work.* 
To go a step farther, it is probable that enzymes do not exist 
in the tissues as such, but in their parent zymogens, the enzymes 
being set free by a suitable extractive and in suitable media. 
* In my original paper, I have discussed the questions more fully. 
