7 6 Proceedings of Royal Society of Edinburgh. [sess. 
the vessel or test tube in which the solution is contained 
plugged), should possess no reducing properties at the end of that 
time. Fehling’s solution must be pure, and not alter in colour on 
boiling. With these precautions we are able to say, definitely, 
if the starch solution, plus X, reduces Fehling’s fluid, that the 
extract itself has reducing properties, or that the starch has been 
converted into a substance that reduces Fehling’s fluid. The 
first point is settled by testing the extract itself. If this has no 
reducing property, we may conclude that the starch solution has 
been altered by a substance which is present in X, which can 
reduce Fehling’s fluid. 
4. The presence of organisms in the tissues — 
This question presents itself as we are aware that organisms 
and their ferments are capable of creating changes in starchy 
and proteid foods in a closely similar way to those caused 
by the unorganised ferments or enzymes that exist in the 
tissues. There are many chemical tests by which we may 
distinguish between the two classes of ferments, such as the use 
of peroxide of hydrogen, borax, salicylic acid (OT per cent.), 
thymol (0*5 per cent.), carbolic acid (0 - 5 to 1 per cent.), 
chloroform, and others, yet we are compelled to admit possible 
results depending on the existence of an organised which 
may be confused with those due to an unorganised ferment. 
It is necessary to make sure that no organisms enter during 
the preparation of the tissues. There must be no putrefactive 
change in the tissues under investigation, or in the fibrin 
itself. All beakers and test tubes must be sterilised, and before 
submitting their contents to the action of heat they must be sealed 
and plugged. 
The organisms themselves are killed during the process of 
extraction and immersion in alcohol, but we have not to consider 
only the organisms, as they may be capable of liberating ferments 
or enzymes, which will be taken up by a suitable extractive. 
By the use of antiseptics we avoid this difficulty. 
Although I never used antiseptics (as I intended to observe the 
results on the tissues unaltered), I hope in a future research to 
compare the results I have obtained with those in which antiseptics 
such as thymol or salicylic acid will be used. 
