668 TRANSACTIONS OF SECTION M. 
these depends upon the ratio of the soil to the water used for extraction. 
Equal parts of soil and water—that is, 100 grams 6f soil and 100 c.c. of water— 
generally give the maximum toxic effect. 
The toxic effect is not evident after rain, but becomes pronounced after a few 
days of dry weather. Similarly, a soil which has been extracted with water, 
and found to be toxic, will, upon further extraction, give a nutritive extract. 
If the same soil, after extraction, be incubated at 22° for some time and then 
extracted with water, the extract will be found to be toxic. Thus toxins are 
developed upon incubating a nutritive soil. 
While the extracts of soils show an enhanced nutritive effect after boiling, 
those of the subsoil become more toxic. It appears, therefore, that there are 
at least two kinds of toxins in soils—one, predominating in the soil, is thermo- 
labile; the other, predominating in the subsoil, is thermostable. 
The action of the volatile antiseptics upon soils is to so alter them that, while 
before treatment they yielded extracts directly bacteriotoxic, after treatment the 
extracts became nutritive. ‘Thus the partial sterilisation of soils, whether by 
heat or by volatile antiseptics, causes them to give extracts, in which there can 
develop a greater number of bacteria. 
2. A Review of Work on Soil Inoculation. 
By J. Goupine and H. B. Hurcuinson. 
Since the introduction of pure cultures of nodule bacteria for soil inoculation 
by Nobbe and Hiltner in 1895 a vast number of field experiments has been 
carried out in different countries and with a great variety of inoculating 
material. 
The results of such experimental work were in the first instance most 
discouraging, and it is only within the last few years that the conditions deter- 
mining success or failure have been adequately recognised. During this time 
the relations existing between the host piant and the nodule organism and 
between the organism and artificial media used for cultivation in the laboratory 
have been studied in detail, and in the light of these investigations it is not 
surprising that failure attended much of the preliminary and often haphazard 
field work. Experience has shown that it is not sufficient to have a pure and 
active culture in order to attain success in soil inoculation, but that the soil 
itself shall be suitable for the growth and continued existence of the introduced 
organism, and that the supply of mineral nutrients shall not be the limiting 
factor in the growth of the plant. Liming has been required in many cases, 
and with a proper recognition of the now known essential conditions the number 
of successful cases of inoculation trials has steadily increased during recent years. 
Comparative work with pure cultures and inoculation by means of soil which 
has previously carried a specified leguminous crop have shown in the majority 
of cases the superiority of the latter, and cultivation in the laboratory has 
latterly included the use of soil media or soil itself, since the organism appears 
to retain its power of infection to a greater extent in this than in other media. 
The use of pure cultures possesses advantages on the score of cheapness and 
convenience, which are sometimes of distinct value, and recent work especially 
has shown the danger attending transference of plant diseases in soil used for 
legume inoculation. The relations attending infection of the plant and subse- 
quent mutual existence are very complex, and future experimental work in 
preparing cultures must aim at reproducing these conditions in order to permit 
of the production of cultures in active growth and possessing great virulence. 
Such work, however, involves accurate scientific control if it is to be of 
permanent benefit to science and agriculture, and in itself would tend to check 
the production of commercial cultures of doubtful origin and hypothetical value. 
3. The Effects of Caustic Lime and of Chalk on Soil Fertility. 
By H. B. Hurcuinson and K. MacLennan. 
Bacteriological, chemical, and pot-culture investigations with the two forms 
of lime have shown their action on the soil to be essentially different. The 
