April 4, 1913] 



SCIENCE 



521 



i. e., we have sometimes found ciliates and 

 amosbffl in soils in which the detrimental fac- 

 tor had been put out of action, but our pres- 

 ent methods do not enable us directly to dis- 

 criminate between protozoan cysts and active 

 forms, nor to estimate the numbers present, 

 nor, on the other hand, to determine how 

 completely the detrimental factor is put out 

 of action. But in general the parallelism be- 

 tween the detrimental factor and the soil pro- 

 tozoa is so complete that we are justified in 

 provisionally regarding protozoa as the detri- 

 mental organisms we have been seeking. 



Such is a short statement of the main 

 lines of the work. I have omitted the sub- 

 sidiary issues: the vain search for baeterio- 

 tosins,* for evidence of bacterial stimulus, of 

 improvements in the bacterial flora, etc. The 

 identification of the detrimental organisms 

 with the soil protozoa is provisional only; in 

 the nature of the case a rigid proof would be 

 very difficult even if it were possible. 



I now turn to some of the criticisms that 

 have been passed on this work by my Ameri- 

 can colleagues. Dr. Jacob G. Lipman at the 

 New Jersey Station, in conjunction with 

 Messrs. Blair, Owen and McLean, carried out 

 some experiments," the results of which they 

 consider to be in direct opposition to ours. 

 They added pasteurized and untreated soil in- 

 fusions respectively to mixtures of dried 

 blood and sterilized soil (heated under a 

 pressure of 1.5 atmospheres of steam). After 

 seven days the pasteurized infusions had in- 

 duced the formation of no more ammonia than 

 the untreated infusion. These results, they 

 say, " do not bear out Russell and Hutchin- 

 son's contention as to the part played by pro- 

 tozoa in depressing the activities of soil bac- 

 teria." 



* This result is not necessarily in contradiction 

 with those obtained by the Bureau of Soils. I 

 understand that Dr. Schreiner's toxin is obtained 

 from badly drained, badly aerated soils deficient 

 in calcium carbonate: our soils, on the other hand, 

 were well drained, well aerated and well supplied 

 with calcium carbonate. 



'Bull. 248. 1912. 



The argument is ingenious, but it does not 

 appear to us to bear on the question. In the 

 first place, soil sterilized by heating under a 

 pressure of 1.5 atmospheres has undergone 

 very considerable decomposition. We have ob- 

 tained evidence that such highly heated soil 

 is altogether different from normal soil as a 

 medium for the growth of microorganisms. 

 Failure of protozoa to develop in the highly 

 heated soil would be no evidence at all of 

 their inability to develop in ordinary soil. As 

 a matter of fact the nitrifying organisms do 

 not seem to have developed; would Dr. Lip- 

 man argue that the results "do not bear out 

 the usual contention as to the part played by 

 the nitrifying organisms in the soil " ? Sec- 

 ondly, even if the detrimental organisms 

 could develop in highly heated soil they were 

 not given the chance: we have never observed 

 any development in anything like so short a 

 period as seven days, our experiments have 

 always been continued much longer. Lastly, 

 the action of the detrimental organisms is to 

 keep down the numbers of bacteria. Now the 

 rate of ammonia production is not necessarily 

 a measure of bacterial numbers and therefore 

 affords no rigid test of the activity of the 

 detrimental organisms. 



Dr. G. E. Stone, of the Massachusetts Ex- 

 periment Station," who has had great experi- 

 ence of soil sterilization and informs us that 

 he has " experimented with practically every- 

 thing there is in this line," is convinced that 

 protozoa " have little or no part in account- 

 ing for the increased number of bacteria in 

 our soils." The evidence is based on some ex- 

 periments by Messrs. Lodge and Smith. De- 

 coctions were made of untreated soil and of 

 soil heated for 45 minutes to 250° F. ; into 

 each of these decoctions soil bacteria were in- 

 troduced. Greater bacterial development oc- 

 curred in the decoction of the sterilized soil 

 than in the decoction of the untreated soil. 

 (A subsoil behaved differently.) The authors 

 state that protozoa were absent and that the 

 results must be due to other causes. With 

 this I entirely agree; a decoction of a highly 



• Twenty-fourth Annual Report, 1912. 



