The Nitrifying Ferments of the Soil. 711 
received opinion at that time that only plants famished with 
green leaves or cells are capable of obtaining their carbon from 
the carbonic acid of the air, and that all fungi, microscopic or 
. otherwise, destitute of green colouring matter, are compelled 
to take their carbon from organic substances ready formed or 
in process of decay. It certainly did not occur to the writer 
i that the nitrifying microbes could dispense with this supply 
I of carbon altogether, but he believed the merest accidental 
traces to be sufficient, and especially recommended boiled pure 
well water, with the addition of a little potassium phosphate, 
I as the most suitable medium for cultivations, containing as it 
i does lime and all the necessary mineral food, with but little 
' organic matter, and that incapable of encouraging most 
' foreign bacterial growths. This was actually the medium in 
I which Winogradsky subsequently obtained his first approach 
' to pure cultures. 
t The systematic attempt to cultivate the nitrifying bacteria 
' by the methods in vogue amongst bacteriologists for all hitherto 
I known microbes led in Winogradsky 's and other hands to some 
I remarkable results. The gelatine method of obtaining pure 
I cultivations of a particular microbe from a medium contain- 
ing several is the one most often resorted to. In principle it 
consists in inoculating a slab of solidified nutrient gelatine, 
containing all materials most favourable for the sustenance of 
bacteria, and carefully sterilised by heat and preserved in 
sterilised tubes, with a thin streak of inoculating material on 
the end of a clean platinum wire. Oi subsequently keeping 
the slab in a warm chamber, the isolated spores introduced with 
the droplet of liquid grow in isolated spots on the gelatine, 
forming little colonies of microbes, readily distinguished one 
from another by their appearance ; on re-inoculating a suitable 
sterilised solution from one of these colonies, a pure cultivation 
of that particular microbe is usually obtained. 
Heraeus, isolating in this way four species of microbe from a 
nitrifying solution seeded with garden soil, and testing them by 
inoculating them into fresh ammoniacal solutions, claimed 
nitrifying powers for them all ; he went even farther, and 
claimed the same powers for several disease-producing microbes 
which had been isolated by the labours of pathologists. It 
seems certain that Heraeus did not produce real nitrification 
with any of these, but mistook the traces of nitrous acid natu- 
rally found in solutions exposed to the air for products of their 
activity. Warington, examining in this way four organisms 
isolated on gelatine from nitrifying solutions or soil, and twenty 
others from other sources, failed to find any of them capable of 
