PRESIDENT’S ADDRESS. 45 
waves on the film, and that on development the silver is 
deposited between the nodes; viewed in the usual way, 
they are apparently ordinary negatives, but viewed at the 
requisite angle such plates exhibit the natural tints. 
Hence the production of nature-coloured photographs is 
still a subject for investigation, for what is generally under- 
stood by the term has not yet been attained. 
AGRICULTURAL CHEMISTRY AND SOME CHEMICAL EFFECTS OF 
BACTERIA. 
The application of chemistry to agriculture has had a 
most marked effect upon the productiveness of the soil. 
Without going into details, the cultivation of the sugar-beet 
may be referred to. The original beet only yielded 2 or 3 
per cent. of sugar, but now, by careful selection, cultivation, 
and treatment of the juice, beets grown in Germany yield 
10, and even 15 to 18 per cent. of sugar. The latter is 
about equal to that from the sugar-cane. It is interesting 
to note that the amount of sugar yielded by the beet stands 
in close relation to the amount of potassium salts present. 
Beet-sugar is said to be now cheaper in Germany than flour. 
Bacteria seem also to take a very important part in opera- 
tions which have been considered as due solely to chemical 
action. 
In the curing of tobacco leaf, it appears to be a well- 
recognised fact that the presence of certain bacteria is 
necessary for the preparation of leaf of high quality, and 
some manufacturers sprinkle the leaf with pure cultures of 
the requisite bacteria. The chemical changes which take 
place m the manufacture of white-lead by the Dutch process 
are also said to be due in part to bacteria, but this, I think, 
requires confirmation. 
In the manufacture of liquid glue, of wines, beer, etc., 
and the ripening of cheese and butter, the products are due 
to the presence of certain bacteria, and in many cases the 
desired result, flavour, odour, etc., can be obtained and 
controlled by inoculation. By fermenting beer with wine 
