712 
Tlie Nitrifying Ferments of the Soil. 
nitrifying. Dr. and Mrs. P. Frankland, who took up the 
search on the same lines, obtained thirty-three distinct microbes 
in pure cultures from air and water, but not one had any 
nitrifying power. Adametz similarly isolated twenty-two, and 
Frank, a number of organisms from soil, and tried them with 
similar negative results. To these and other negative results 
of other observers must be added the gelatine cultures of Wino- 
gradsky, who has published during the last two years, in the 
Annates de I'lnstitut Pasteur, the most searching and the most 
successful series of memoirs on this subject, and has at last 
cleared away much of the mystery surrounding it. 
Having formed the idea that the failures recorded were 
possibly due to inability of the nitrifying organism to grow on ilie 
gelatine slabs, Winogradsky proceeded to try Avhether by culti- 
vating successive generations in ammoniacal liquids favourable 
to nitrification and unfavourable to other fermentations he could 
not get rid of all organisms able to grow on gelatine, whilst still 
preserving his nitrifying organisms intact. Very soon abandon- 
ing organic matter as an ingredient of his liquid medium, and 
using Lake Zurich water, with no addition but the ammonia 
salt, a little potassium phosphate, and some magnesium carbon- 
ate, he found, after successive inoculations extending over several 
months, that only five species which could be isolated on gela- 
tine persisted in living in the medium employed, and not one of 
these would start nitrification. But the carbonate of magnesia 
at the bottom of the flasks had altered in appearance ; instead 
of being powdery it had become gelatinous or flocculent, and 
could not easily be shaken up with the liquid ; under the micro- 
scope, particles of carbonate were seen to be invaded with masses 
of an oval bacterium, and bits of this deposit, inoculated into 
fresh solutions, were far more powerful in exciting nitrification 
than a drop from the middle or surface of the liquid. Here, 
then, was probably the nitrifying organism comparatively pure, 
and on shaking up a little with water and inoculating gelatine 
slabs with the mixture, it was found that only colonies of the 
non-nitrifying microbes already mentioned slowly grew and 
invaded the inoculated spots — in other words, the oval bacterium 
of nitrification would not grow on the gelatine, and it was still 
adulterated by others that voiilcl. 
It was only at this stage that Winogradsky abandoned the 
lake water in favour of the purest distilled water, and banished, 
as far as possible, every trace of organic matter as affording food 
for these foreign organisms. Specially purifying all his ma- 
terials from every trace of organic matter, he found that nitri- 
fication went on as well and rapidly as ever, whilst even in the 
