PROCEEDINGS OF SECTION K. 651 



effect of partial sterilization by heat or antiseptics upon the growth 

 of the crop is attributable to the larger proportion of ammonia 

 present in the soil after such treatment. These authors explain 

 this phenomenon as follows : — ■ 



Probably in all soils, certain larger unicellular organisms (Pro- 

 tozoa) are present which feed on the bacteria concerned in the for- 

 mation of soluble nitrogen compounds, and keep them in check. 

 If the soil is partially sterilized by heating for a short time to the 

 temperature of boiling water, or by subjecting it to the action of 

 vapours such as chloroform, bisulphide of carbon, toluene, &c., 

 (such vapour being subsequently removed by spreading the soil out 

 in a thin layer, and allowing the vapour to evaporate), the effect 

 is to destroy the protozoa, and probably most of the bacteria as 

 well, but not the spores of the ammonia-producing bacteria. 

 These spores subsequently develop, and in the absence of the hos- 

 tile protozoa, their development proceeds with increased activity, 

 the result being a considerable increase in the soluble nitrogenous 

 plant-food, and a more vigorous crop growth. 



These experiments have, so far, been carried out in the labora- 

 tory. If means are discovered of partially sterilizing the soil in 

 the field, a most valuable method of increasing the fertility of the 

 soil will be placed at the disposal of the farmer. 



Indeed, experiments in this direction have been recently carried 

 out by E. J. Russell and J. Golding {Journal Agricidtural Science, 

 Vol. 5, p. 27) on " sewage-sick " soils. They find that " sewage- 

 sickness " is an abnormal development of the factor harmful to 

 bacteria (protozoa) always present in ordinary soils, and that the 

 loss of efficiency in the purification of sewage in such soils is due 

 to the hindrance of development of bacteria. Small land-filters 

 were made in the field, some being filled with untreated soil, and 

 others with treated or sterilized soil. The effluents were examined 

 periodically. The untreated samples soon became " sewage-sick," 

 whereas the effluents from the treated filters showed that these had 

 retained their efficiency for months. A further experiment was 

 tried by treating small plots in a similar manner, the plots being 

 then sown with turnips. The crops on the treated plots (especially 

 that treated with toluene) were not only better than those from 

 the untreated, but suffered much less from " finger and toe." 



Further interesting trials are recorded by E. J. Russell and F. 

 R. Petherbridge (ihicL, p. 86) of the action of heat and antiseptics 

 upon sicknes in glass-house soils. In countries where plants like 

 cucumbers and tomatoes are grown under glass, the soil is found 

 to be unsuitable for the growth of these plants after a short time, 

 sometimes after the first crop. The soil used is therefore thrown 

 away, and as it is necessary to enrich it very much with manure, 

 and to expend much time and labour on its preparation, this is a 

 very wasteful operation. The authors find that previous steaming 



