612 



SCIENCE 



[N. S. Vol. XXXVI. No. 932 



photographs of which have been used most 

 extensively to illustrate popular articles on 

 the subjects, can have no part whatever in 

 disposing of beneficial bacteria or influ- 

 encing in any appreciable way the fertility 

 of the soil. For it is found that the cili- 

 ated protozoa which are so characteristic a 

 feature of cultures made from soil, exist 

 only in the encysted stage in natural soil 

 conditions. There remain, of course, the 

 amoebfe and flagellates, about the condition 

 of which in soil we are not certain as yet. 

 But the fact that all of these organisms are 

 able, within a short time after being re- 

 moved by disinfectants, to reestablish them- 

 selves in soils, would seem to indicate that 

 even though they might have some direct 

 effect upon the bacterial content of the soil, 

 the removal is so transient that the effect 

 on crop production is negligible. This is 

 no place for figures, but if it were I could 

 show as the result of tests, extending over 

 a wide field, that the number of protozoa, 

 including flagellates, ciliates and rhizo- 

 pods, existing in the soil three days after 

 treatment with various percents of toluol, 

 carbon bisulphide, etc., may equal or even 

 exceed the number originally present. 



Koch and Fred at the Agricultural In- 

 stitute of the University of Gottingen, since 

 the appearance of Goodey's paper, have 

 each published independently upon the 

 effect of ether and carbon bisulphide on 

 lower and higher plants and conclude that 

 for both the micro-flora of the soil and the 

 crop it bears, the beneficial effect is purely 

 stimulative — simply the old idea of all 

 poisons being beneficial to growth if suffi- 

 ciently dilute. 



Greig-Smith, in spite of the apparent 

 refutation of the toxin theory of Eussell 

 and Hutchinson, returns to it as affording 

 the best explanation of the observed re- 

 sults. He claims to have extracted from 

 soil a substance which is filterable through 



porcelain and which is toxic to bacteria. 

 This toxin thus retards the growth of 

 higher plants by the destruction of bene- 

 ficial bacteria, but in turn is destroyed by 

 the application of heat or volatile anti- 

 septics. An additional effect of these 

 agents is upon the so-called "agricere," 

 which, according to Greig-Smith, is a mix- 

 ture of saponifiable and unsaponifiable 

 bodies, coating or waterproofing particles 

 of soil. When heat or certain wax solvents 

 are added to the soil, they alter the distri- 

 bution of the earth wax, carrying it to the 

 surface and causing it to segregate on the 

 points of the soil particles. The beneficial 

 effect of the removal of the waterproof 

 covering is of course that the constituents 

 of the soil are more easily attacked by the 

 bacteria and rendered available for plant 

 nutrition. 



Bottomly, before the British Association 

 this summer, confirmed to a certain extent 

 the work of Greig-Smith by demonstrating 

 the injurious effect of the "bacteriotox- 

 ines" upon the germination of seeds and 

 their subsequent growth, the harmfulness 

 of which could be prevented by first heat- 

 ing the soil. 



Without further reference to contradic- 

 tory results obtained by various investiga- 

 tors since the announcement of Russell and 

 Hutchinson, experiments in my own labo- 

 ratory indicate that the matter is probably 

 incapable of being satisfactorily explained 

 by any of the single factors which have 

 been suggested. The one fact which does 

 seem to be fairly well established is that 

 the temporary removal from the soil of 

 the protozoa has but little bearing on the 

 problem. Neither is it by any means cer- 

 tain that the use of heat or antiseptics is 

 universally favorable to all crops on all 

 kinds of soil and it seems probable that the 

 character of the soil, as well as the kind of 

 crop, will have to be taken into considera- 



