TRANSACTIONS OF SECTION M. 667 
Of the non-protein nitrogen, 10 per cent. is driven off by distillation with 
magnesia and 18 per cent. is precipitated by phosphotungstic acid. 
After hydrolysis of the solution of non-protein nitrogen with dilute acid for 
two hours, the amount of nitrogen distilled over with magnesia is 10 per cent. of 
the non-protein nitrogen, but if now the hydrolysis be repeated another 10 per 
cent. of the non-protein nitrogen distils over. If hydrolysis be long continued, 
the amount of nitrogen that can be distilled over with magnesia rises to over 
30 per cent. of the non-protein nitrogen. 
If the non-protein solution be hydrolysed for two hours with dilute acid, then 
nitrous acid liberates nitrogen corresponding to 66 per cent. non-protein nitrogen. 
If, however, the hydrolysis be repeated long enough the liberation of nitrogen by 
nitrous acid diminishes to zero. 
With Sorensen’s method of titration no fixation of formaldehyde by amino- 
groups occurs. 
The attempts to isolate amino- acids invariably resulted in the discovery of 
traces. 
The amount of purin nitrogen present is small, less than one per cent. 
The following Papers were then read : 
1. Bacterial Toxins in Soils. By R. Greta-Smrru, D.Sc. 
If the soil-water is considered as a medium for the growth of bacteria, it 
should contain not only the nutrients that favour bacterial growth but also the 
waste products of their vital activity. And if we reason from what we know 
about the growth of bacteria in other media, we should expect that some of 
these waste products are injurious to the bacteria producing them. Further- 
more, in a mixed flora, certain groups should produce injurious substances in 
greater amount, and these should differ in degree in their action upon bacteria 
of their own group or of other groups. For convenience, these injurious sub- 
stances are called toxins. Certain investigators deny the presence of toxins 
in soils, although they admit the presence of inhibiting substances. It is 
difficult to account for the discrimination. 
The multiplication of bacteria in the soil will among other conditions depend 
upon the relative preponderance of the nutrients over the toxins; and, with 
the other conditions remaining constant, an ultimate equilibrium should be 
established between the nutritive and the toxic effects. An alteration of the 
other conditions will disturb the equilibrium, and the bacteria will increase or 
decrease until another balance is established. 
In demonstrating the presence of bacterial toxins in soils, I have made use 
of aqueous extracts of soils which after filtering through porous porcelain have 
been seeded with known quantities of bacteria. Generally, Bac. prodigiosus has 
been employed as a test organism. It is more sensitive than mixtures of soil 
bacteria, and is easily grown, detected, and counted. Tests have shown that 
extracts which destroy Bac. prodigiosus retard the growth of mixed soil-bacteria. 
We are justified in considering that an extract which destroys Bac. prodigiosus 
is also capable of destroying some of the soil-bacteria. 
The bacterial toxins are not always easily demonstrated, as they are fre- 
quently overshadowed by the soil-nutrients, but investigation has pointed out 
some of the conditions under which they may not be expected to show a direct 
action in soil-extracts. For example, they are destroyed by exposing the 
soil to the sun, by heating the soil, by storing the soil in the air-dry condition ; 
they decay rapidly in aqueous solution, and are destroyed upon boiling. They 
are soluble in water and are washed out of the soil by rain. Direct evidence 
of their presence should not, therefore, be expected in arid soils, in soils during 
a drought or in soils after rain. Much of the so-called fertilising effect of the 
sun may be due to the destruction of the soil-toxins. Indirect evidence of their 
presence is easily obtained by boiling the soil-extract, seeding it with bacteria, 
and comparing the growth with that obtained in the unboiled extract. A 
greatly increased growth of bacteria is usually obtained in the boiled extract. 
A direct diminution is only obtained under certain conditions. These have 
not been fully investigated, but enough has been done to show that one of 
