i6o 



NATURE 



[April 17, 1913 



explaining their structural relationships to human 

 1 ices .us inheritances from a common basal stock. 

 It will be thus seen that Prof. Sergi is the 

 arch-priest of that heterodox doctrine — the mul- 

 tiple origin of closely allied species and genera. 

 His faith is more robust than that of the majority 

 of his colleagues. He accepts implicitly Ame- 

 ghino's speculations concerning the independent 

 origin of mankind in South America. Although 

 the reviewer regards the majority of Prof. Sergi 's 

 opinions as ill-founded, he is only too willing to 

 admit that it would be presumptuous, in the 

 present state of our knowledge of extinct forms, 

 Ui refuse them a most careful investigation. 



A. K. 



Vicious Circles in Disease. By J. B. Hurry. 

 Second edition. Pp. xiv + 280. (London: 

 J. and A. Churchill, 1913.) Price 75. od. net. 

 In the issue of Nature for May 18, 191 1 (vol. 

 Ixxxvi., p. 374), an extended review by Sir T. 

 Clifford Allbutt was published of the first edition 

 of Dr. Hurry's book. The present edition has 

 been revised, and six new chapters have been 

 added in the hope of covering the ground more 

 adequately. Most of the material of these addi- 

 tions has appeared already in the medical Press. 



LETTERS TO THE EDITOR. 

 [The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Soil Fertility. 



f)K. Russell begs the whole question in two lines 

 of his letter in Nature of January 16, when he ter- 

 minates para. 7 with "the increased gain in plant 

 growth on such highly heated soils can be largely 

 attributed to this cause," viz. to the formation of 

 ammonium and other simple soluble nitrogen com- 

 pounds on heating soils to 170°. 



If this were true, then the effects of heating soils, 

 whether to the temperature of "partial sterilisation, " 

 viz. q8° (as in Dr. Russell's experiments) or (as in 

 niim) to 170 , could be imitated by adding in, say, 

 daily doses, suitable solutions containing ammonium 

 'impounds and nitrates. 



I have repeatedly tried this with various combina- 

 tions of salts, both in pot experiments and in the 

 field, and have invariably found that the increased 

 growth due to heating' the soil previously was never 

 evi 11 approached in extent by that in any of the plots 

 10 which tin- manure- wen- added. 



It appears to me that the increased growth in Dr. 

 Russell's experiments can only be safely ascribed to 

 the manufacture of soluble nitrogen compounds by 

 bacteria when in parallel sets of pots and plots the 

 same effect is shown to be produced by artificially 

 dosing unheated soils with such nitrogen compounds. 



F. Fletcher. 



Rewika Ranch. Kyatnbu, British East Africa, 

 March 6. 



I AM not at all surprised that Mr. Fletcher failed 

 fo reproduce the conditions of a strongly heated soil 

 by simplv addinsr freouent doses of ammonium com- 

 pounds to an unheated soil. Soil suffers considerable 

 decomposition when heated to 170 C, and changes 



XO. 2268, VOL. qi] 



markedly in chemical composition, physical prop. ni. s. 

 suitability as a medium for the growth of bacteria, 

 moulds, and other organisms, and as a habitat for the 

 higher plants. Experiments become extraordinarily 

 difficult to interpret when so many factors change 

 simultaneously, and for this reason I have always 

 preferred to adopt very much milder methods, treating 

 the soil with antiseptic vapours (e.g. toluene), or 

 heating to as low a temperature as possible (6o° t& 

 95 C). Here less complication arises, because the 

 decomposition effects are at a minimum, and one can 

 study the various factors one at a time. 



Increases in productiveness equal to those brought 

 about by treatment with antiseptic vapours or heat- 

 ing to 65° C. can be obtained on our normal 

 untreated soils by additions of sodium nitrate or 

 ammonium sulphate. Further, partial sterilisation has 

 failed to bring about increased productiveness when 

 the treated and untreated soils are subsequently so 

 liberally treated with nitrogenous plant food that the 

 nitrogen supply is no longer a _ limiting factor. In 

 "sick" soils, however, there is another limiting 

 factor, the presence of disease organisms and pests, 

 and this also is put out of action more or less com- 

 pletely bv partial sterilisation. Here addition of 

 nitrogenous plant food (which leaves the pests un- 

 affected) does not make the untreated soil equal in 

 productiveness to the partially sterilised soils. We 

 could get no evidence of the toxin suggested by Mr. 

 Fletcher, and, this being the case, I do not see how 

 we shall advance matters by assuming its presence 

 as a third limiting factor. E. J. Russell. 



Rothamsted Experimental Station, Harpenden. 



Induced Cell-reproduction in the Protozoa. 



I was interested in Mr. T. Goodey's letter under 

 the above heading in Nature of March 13, but should 

 like to make a few remarks thereon. Hay infusion, 

 which Mr. Goodey states caused the excystation of 

 Colpoda cucullus, is prepared from dried grass, and 

 here we have the products of cytolysis, and, in conse- 

 quence, should expect the presence of auxetics. \s 

 a matter of fact, any vegetable infusion contains 

 auxetics, the presence of which can be demonstrated 

 by the jelly method on human lymphocytes, as de- 

 scribed by Dr. H. C. Ross, " Induced Cell Reproduc- 

 tion and Cancer " (London : John Murray, 1910). 

 Encysted forms of Colpoda cannot be compared with 

 the winter spores of Polytoma, as in Colpoda there 

 is, so far as I can gather from Mr. Goodey's letter, no 

 conjugation prior to the encystment, and consequently 

 no real development is necessary for the excystation, 

 but only rupture of the cyst-wall. In Polvtoma, how- 

 ever, the cytoplasm within the spores has to undergo 

 several- complex changes, leading ultimately to division 

 of sarcode, formation of envelopes round the products 

 of division, and the development of flagella. Thus, 

 I take it that in Colpoda there is no reproductive 

 process in the excystation, and consequently no neces- 

 sity for auxetics; anything that will cause the rupture 

 of the cyst-wall being sufficient, although, as already 

 shown, auxetics were certainly present in the hay 

 infusion. 



With regard to the "pure distilled water," Mr. 

 Goodey should remember that this is pure only so 

 long as he adds nothing else to it. Directly organ- 

 isms are added, auxetics would be present, as, apart 

 from the fact that some of the culture fluid would 

 be introduced with the organisms, even if this were 

 not so, auxetics would be present, as there would be 

 necessarily some death-rate. The same phenomenon 

 also occurs in pond Amcebfe, the encysted forms of 

 which ran also be caused to undergo excystation bv 

 incubation with distilled water. 



