1899-1900.] Dr J. S. M‘Kendrick on Enzymes in Tissues. 77 
The only tissues where such a difficulty really arose were those 
of the intestines of the rabbit and child, certain of the pathological 
tissues, in sputum and in the post-mortem tissues. In sputum, 
no doubt, pyogenic organisms exist in great numbers. The post- 
mortem tissues were removed in less than twenty -four hours after 
death, and were at once placed in absolute alcohol. The other 
tissues were fresh, and were removed, powdered, and placed in 
absolute alcohol within a few hours after their removal. 
In the intestines putrefactive bacteria are always present, but 
the greatest care was taken in stripping off the mucous membrane 
of the bowel, and in washing it freely in running water before 
mincing and placing it in alcohol. The fibrin which was used 
was fresh, and contained no putrefactive organisms. 
I admit that no means in the way of antiseptics have been 
used to distinguish whether the results depended on the action 
of the unorganised or organised ferments ; but I consider that in 
most cases the results have not depended upon the organised, 
but upon the unorganised ferments or enzymes, which play such 
an important part in the process of digestion. 
5 . The cleavage of proteids by acids alone — 
Fibrin is unaltered by the action of pepsin alone, but in the 
presence of hydrochloric acid rapid digestion takes place. A 
weak solution of the acid itself has the power of causing the 
fibrin to swell up and become translucent, and to produce an 
acid albumin, or even albumoses and peptones. 
Do we know, then, whether the peptones that are produced 
in various experiments depend upon the activity of an enzyme in 
conjunction with HC 1 , or from HC 1 itself? 
The biuret reaction is a fairly distinctive test. 
If pepsin has been at work, then a rose-pink coloration results,, 
but, if not, a violet coloration is produced. 
6 . The coagulation of milk — 
A certain amount of coagulation occurs from heat alone, but 
the coagulation which thus occurs is very different from the form 
of clot produced by the action of rennin. 
