26 
Prevention Act, I mention my wish to develop germs of 
living things in water as a test for purity. The quotation 
is from a paper printed by this Society in 1867. The results 
were correct and useful, but not striking enough to attract 
much attention, although I think chemists have not been 
sufficiently active in using the microscope. Having long 
seen its importance, I confess to having done too little with 
it. In a report under the Alkali Act during the year 1873 
I mention a second attempt to render the existence of 
organic matter more perceptible by using the air washings 
to act upon sugar, and after many trials I was disappointed ; 
still I came to the conclusion “ that the air of a town influ- 
ences fermentation to a certain extent.” — 10th Report, p. 43. 
I neglected this development also too much, but Dr. Koch, 
of Berlin, has shown us how to preserve the indications of 
organic vitality by the use of gelatine. I believe he was 
the first to use it. It is from Dr. Koch, at any rate, that I 
learned the use of gelatine. About 2J per cent of gelatine 
well heated in a little water is mixed with the water to be 
tested, and the mixture forms a transparent mass which is 
not movable like the water itself. When soluble or un- 
observed matter develops from the organic matter of the 
waters and makes itself visible in a solid and insoluble form, 
it does not fall to the bottom, but each active point shows 
around it the sphere of its activity, and that sphere is 
observed and remains long. The gelatine preserves to us 
the whole action, so far as the more striking results are 
concerned, and keeps a record, for a time, both of the quality 
and intensity of life in the liquid. I speak at present of 
the more striking effects, which are clear and abundant, 
every little centre of life making itself clear to the eye and 
sometimes expanding its influence to reach both sides of 
the tube. It seems to me now essential that all chemical 
examinations of water should be supplemented by an 
enquiry, like this of Dr. Koch’s, into the comparative 
