522 



SCIENCE 



[N. S. Vol. XXXVII. No. 953 



heated soil is manifestly very different from a 

 decoction of untreated soil; it contains much 

 larger quantities of dissolved substances and 

 may be expected to behave differently as a 

 medium for bacterial development. The ex- 

 periment proves conclusively that heating a 

 soil to 250° F. causes decomposition, but I can 

 not see that it helps us to find out what is 

 going on in an unheated soil. The authors 

 go on to say that protozoa are " uncommon in 

 their soils" and "very few forms were 

 found." It would be interesting to find what 

 is the difference between their soil conditions 

 and those at Michigan where Dr. Eahn' found 

 protozoa of the same types occurring in num- 

 bers of the same order per gram as we find at 

 Eothamsted. 



Professor G. T. Moore, writing in Science," 

 disagrees wholly and absolutely with our 

 work; indeed he thinks that in the tangled 

 maze of microbiological problems "the one 

 fact which does seem to be fairly well estab- 

 lished is that the temporary removal from the 

 soil of the protozoa has but little bearing on 

 the problem." We should not feel that we 

 had lived in vain if we had merely been the 

 humble instruments by which such a proposi- 

 tion was established, but again we are not 

 satisfied as to the evidence. Professor Moore 

 asserts that soil protozoa are not killed by 

 toluene, carbon disulphide, etc., but are only 

 temporarily depressed, and after three days 

 their numbers may equal or even exceed those 

 originally present. Never on any occasion 

 have we observed anything of this kind. 



In an admirable paper" on the effects of 

 heat on the soil Drs. Seaver and Clark attrib- 

 ute to us the claim that the increased pro- 

 ductiveness of heated soils is due to the de- 

 struction of protozoa. We wish to point out 

 that we have always regarded the destruction 

 of detrimental organisms as only one factor 

 in the case, and have fully recognized the ef- 

 fects of the decomposition brought about by 

 the heat. In order to minimize these decom- 

 position effects we generally treat our soils 



^Centr. BaU. Far., 1913, 36: 419^21. 



s November 8, 1912. 



^ Biocliemical Bulletin, 1912, 1: 413. 



with vapors of antiseptics rather than by 

 heat, but here also we do not lose sight of the 

 possibility of other changes being induced be- 

 sides the destruction of life. 



Finally, we may be allowed to remind the 

 reader that the adverse effect of our detri- 

 mental organisms is on the numbers of bac- 

 teria, but that the relationship of bacterial 

 numbers to soil fertility is by no means 

 simple. Fertility is determined by any of the 

 factors capable of limiting plant growth. In 

 some soils it may be the supply of phosphates, 

 of potash, of water that is inadequate; if so, 

 soil bacteria may show little or no connection 

 with fertility. Only when the supply of nitro- 

 gen compounds becomes a limiting factor do 

 the soil bacteria come in, and even then the 

 relationship between their numbers and their 

 activity is not quite straightforward. We 

 have traced out this problem in detail in our 

 paper in the Journal of Agricultural Science, 

 1913, p. 152. 



We do not underrate the complexity of soil 

 fertility problems and, above all, we do not 

 assert that our destructive organisms are the 

 only things involved in the matter, but we do 

 claim that they are an important factor. Our 

 only hope of getting any further with the 

 complex problems of the soil is to study the 

 factors one at a time. We must not be con- 

 fused by the circumstances that other factors 

 remain to be studied, nor, on the other hand, 

 must we lose sight of the possibility that these 

 other factors may vitiate some of our experi- 

 ments. 



E. J. KUSSELL 



Eothamsted Experimental Station, 

 Harpenden, England 



TWO additions to the mammalian fauna of 



MICHIGAN 



The northern pine vole, Microttis pinetorum 

 scalopsoides (Audubon and Bachman) has ap- 

 parently not been recorded from Michigan, 

 and up to last year no Michigan specimen had 

 been secured by the museum. In April, 1912, 

 a specimen (No. 42,558, Museum of Natural 

 History, University of Michigan) was taken 

 by W. A. Brotherton, near Eochester, Oak- 



