96 



NA TURE 



[March 24, 1910 



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.] 



Fertilising Effect of Soil Sterilisat on. 

 With further reference to the work of Messrs. Russell 

 and Hutchinson on soil sterilisation {Journal of Agri- 

 cultural Science, October, 1909), it may be interesting to 

 record some information of which I have recently become 

 possessed. 



Some of the large growers of cucumbers, tomatoes, &c., 

 under glass for the London market have for some little time 

 adopted the plan of injecting jets of steam into their soil 

 before planting, not with any view of increasing its fertility, 

 but with the view of destroying slugs, insects, &c. In 

 the experience of some growers the productivity of the 

 soil after steaming has become so greatly increased that, 

 if anything like the usual quantity of stable manure is 

 mixed with the soil, the plants grow with such rank 

 luxuriance as to spoil their bearing capacity, exhibiting 

 all the symptoms that would be expected as the result of 

 a heavy overdose of nitrogen. 



This experience has been communicated to me by 

 growers who were previously unaware of the Rothamsted 

 work. At the moment they were feeling in somewhat of 

 a dilemma : if they did not steam the soil they suffered 

 from insect pests ; if they did steam it they were obliged 

 to curtail the supply of stable manure, at the expense of 

 lowering the subsequent soil temperature, which is 

 normally maintained at a high level by the fermentation 

 of the manure. \o doubt means may be found of adjust- 

 ing the various conditions satisfactorily, but meantime 

 the observation appears to afford striking independent 

 confirmation on a practical scale of the indirect fertilising 

 effect of partial sterilisation in killing off the phagocytes 

 or protozoa which normally keep down the numbers^ of 

 those bacteria the task of which is to turn organic nitrogen 

 into plant food. Bernard Dyer. 



17 Great Tower Street, London, E.C., March 15. 



Certain Rpactions of Albino Hair. 

 In a note in the Journal of Physiology (vol. xxxviii.) 

 on the chemical nature of albinism, Mr. Mudge describes 

 some interesting observations which he made upon rats' 

 skins. Starting with the presumption, based upon the 

 work of Miss Durham and Cu^not, that an albino carries 

 a chromogen and lacks the ferment necessary to produce 

 pigment from it, and supposing that fermentation is a 

 process of oxidation or reduction, Mr. Mudge argued that 

 it might be possible to produce pigment artificially bv 

 means of an oxidising or reducing agent. He found bv 

 experiment that immersion of albino rat skins in a solu- 

 tion of 10 per cent, formalin and 70 per cent, alcohol in 

 equal volumes resulted in a " vivid yellow colour " in the 

 hairs ; he further states that these coats, when washed in 

 water and immersed in H,0, (20 vols.), become changed 

 in colour from vivid yellow'to'a " brownish tint " in about 

 twenty-four hours. He adduces arguments to show that 

 the coloration is due to the presence of a specific body in 

 the hairs diffused through the keratin, and not to mere 

 reaction between the keratin and the formalin. 



I have repeated these experiments with various skins. 

 In the case of the single albino rat skin which I used, the 

 vivid yellow was obtained immediately on immersion in 

 the formalin mixture. The change to brown in HjO, was 

 not obtained, but complete decoloration resulted from 

 immersion in this reagent. Prolonged immersion in the 

 formalin mixture also produced almost complete decolora- 

 tion. 



With guinea-pig albinos carrying, respectively, black, 

 chocolate, and red, negative results were obtained, as they 

 were also with a single mouse skin. 



What struck me as particularly interesting in connection 

 with the yellow colour produced by the formalin mixture 

 in the coat of the albino rat is the fact that it is a peculiar 

 - canary-yellow, which I remember to have seen elsewhere 

 among mammals only in members of the stoat family when 

 the winter whitening is incomplete. A piece of pale yellow 

 stoat fur acquired a much more intense yellow colour as 

 NO. 2108. VOL. 83] 



a result of twenty-four hours' immersion in the formalin 

 mixture ; a similar piece was decolorised by HjOj. There 

 can thus be little doubt that the yellow body produced 

 artificially in the fur of the albino rat is a substance 

 similar to the yellow pigment of the stoat's winter coat, 

 and therefore probably represents a stage in the reduction 

 of the pigment to the condition in which it exists in the 

 white hairs. 



Miss Durham tells me that it is a well-known fact that 

 albino rats do not remain pure white if they are exposed 

 to the action of light. Just as darkness is necessary for 

 the production of a pure white coat in the rat, so a certain 

 degree of cold seems necessary in the case of the stoat 

 tribe, though in their case a change to a warmer climate 

 does not at first prevent the usual colour-change in winter. 

 Thus Eric Parker, in " The Book of the Zoo," points out, 

 concerning a certain foreign pine-marten, that " the first 

 winter he spent in the Garden his fur turned almost white 

 to match the snows he would naturally have expected. 

 The last two winters it remained brown, though it has 

 lightened considerably towards yellow." This repetition 

 of a periodic act without the uSti(ia,l stimulus recalls certain 

 phenomena in plants, which Mr. F. Darwin attributes to 

 memory. Igerna B. J. Sollas. 



Nifroare n fixing Bacteii' and Non-leguminous Plants. 



May I be allowed to direct attention to two errors in 

 Mr. Hall's letter in Nature of December 23, 1909? 



Mr. Hall states that " Pseudomonas and .^zotobacter 

 together (1-24) are less effective than when grown 

 separately (0-91 -1- 0-56)." This comparison is incorrect. 

 The fi.xation of free nitrogen by bacteria is esti- 

 mated in terms of milligrams of nitrogen per unit of 

 carbohydrate in the culture solution. Pseudomonas and 

 Azotobacter together give 1-24 N for one unit of carbo- 

 hydrate. Pseudomonas and Azotobacter grown separately 

 give 1-47 N for two units of carbohydrate, hence the correct 

 comparison is :■ — 



Per unit 



Pseudomonas and Azotobacter together = i "240 N 



Pseudomonas and Azotobacter separately: 



^■47. 



:0735 N. 



Hence my conclusion that Pseudomonas and Azotobacter 

 together are more effective than when grown separately is, 

 1 think, justified. 



The second error has reference to a mean experimental 

 error of +10 per cent. Mr. Hall writes: — "By an error 

 which the context rendered sufficiently obvious, I wrote 

 " oats " instead of barley when dealing with Prof. Bottom- 

 ley's first-quoted experiment with soil." May I point out 

 that oats were the only plants mentioned in the " first-quoted 

 experiment with soil "? Even if the increase of barley 

 (13-6 per cent.) be taken, one fails to see how it is 

 " sufficiently obvious " that a mean error of ±10 per cent. 

 more than covers an increase (the lowest of the results 

 quoted) of 13-6 per cent. W. B. Bottomley. 



King's College, Strand, W.C., February 16. 



A Sample of Spurious Correlation. 



Though regretfully unable to do justice to the mathe- 

 matical reasoning of Dr. G. T. Walker in Nature of 

 January 6, I may, perhaps, be allowed to say that it is 

 of the essence of the method that those dots (each express- 

 ing a comparison of two sums of thirty items) tend to 

 arrangement in a straight band, or strip, with fairly de- 

 fined borders. It is expected that future dots will generally 

 come within those limits ; but to affirm this in a given 

 case, to say, e.g., that the next dot will not be below a 

 certain level, is it not, necessarily, to say something quite 

 definite as to the character of the coming season, as that 

 its rainfall, frost days, or other feature considered, will 

 not be below a certain numerical value? If the one state- 

 ment is warranted, so (by the nature of the case) is the 

 other. Thus the essential point seems to me to be 

 whether the past distribution of those dots affords a 

 reasonable clue to their future distribution, and I do not 

 see that my critic throws doubt on this. 



I think (with all deference) that anyone who will give 

 the method a full trial will find it distinctly helpful in a 

 number of cases (I do not say in all). 



Alex. B. MacDowall. 



8 Marine Crescent, Folkestone, January 14. 



