226 



NATURE 



[May 17, 19 1 7 



at every ordinate, so as to provide the data for drawing 

 what 1 will call, for brevity in reference, the "gusto- 

 graph " record. That something in the way of truth 

 has then been obtained appears from the reflection that'a 

 man who had the air acceleration under his control for 

 a given five minutes and a gustograph or acceleration 

 record for some previous five minutes, would be able 

 to reproduce the gusty phenomena of the air for that 

 previous five minutes by controlling the air accelera- 

 tion according to the gustograph record. He would 

 not, of course, necessarily reproduce the actual wind 

 of the previous five minutes, unless he happened to 

 start the five-minute reproduction with the right wind 

 value, but that agrees entirely, I believe, with the 

 distinction there is between gustiness and wind in 

 connection with aircraft. 



As regards the safe " flyability " of the air bv aircraft, 

 I hazard the guess that it may be found convenient to 

 connect it with such a quantity as the maximum gust 

 over a random minutp run of the gustograph, or 

 perhaps with the average gust over the same period. 



The proposal Prof. McAdie mentions — usin^ the ex- 

 ponent of an exponential equation as the measure of 

 the sharpness of a gust — looks easier to apply in 

 examining the influence of particular classes of gust.^ 

 than in obtaining continuous records from instant to 

 instant. For the latter purpose it is, I submit,, desir- 

 able that the gust should be defined by instantaneous 

 conditions, independently of knowledge of things at a 

 finite time either before or after the given instant. I 

 may, however, be misunderstanding the exponential 

 proposal in this connection. 



If principles like those I suggest found acceptance, 

 the question of having standard gustograph instru- 

 ments would soon be likely to arise; for graphical 

 differentiation of anemograph records is tedious, and 

 discouraging to progress. I think gustographs may 

 be designed on two broad principles : in the first there 

 is an anemometer in which the rate of change of the 

 reading is continuouslv recorded, and in the second 

 there is an arrangement of fans and flywheels with 

 torque-recording couplings between. 



I shall be very pleased if what I have written con- 

 tributes to the discussion anything which needed, in 

 any case, to be brought under consideration. 



S. L. Walkdkn. 



London, N., April 25. 



The Preparation of " Blood Charcoal." 



Pure "blood charcoal " is a reagent of consider- 

 able importance to the physiological chemist. It is 

 not only required for the decolorisation of liquids, 

 but also for selective adsorption in an important series 

 of quantitative estimations of animal fluids. 



My stock of Merck's blood charcoal is nearly ex- 

 hausted, and I cannot obtain a supply of any home- 

 made article that is suitable. 



I should be most grateful if any of your readers 

 could give me any information as to the method of 

 preparation of blood charcoal, or the name of a firm 

 that would be willing to manufacture and supply the 

 article. Material as good as Merck's would command 

 a ready sale at home as well as in America, where 

 they have^ had to abandon rapid and accurate methods 

 of analysis owing to the lack of the necessary char- 

 coal. Folin states, in a recent number of the Bio- 

 chemical Journal, that no other charcoal will adsorb 

 creatinine, I have got perfect results with two other 

 specimens of charcoal, but inquiry reveals the • fact 

 that both of them came originally from Germany. 

 Surely our technical chemists can produce arficles as 

 good as those of the Germans. Sydney W. Cole. 



Biochemical Laboratory, Cambridge, May 9. 



NO. 2481, VOL. 99] 



STUDIES IN GENETICS.^ 



(i) pROF. CASTLE was fortunate enough to 

 ^ secure in Peru a number of specimens 

 of a wild species of guinea-pig, Cavia cutleri, 

 Bennett, which is the probable ancestor of the 

 numerous domesticated races which have had their 

 origin in that country and have been introduced 

 elsewhere. He found that this wild species pro- 

 duced completely fertile hybrids when crossed 

 with various races of domesticated guinea-pigs, 

 and the results of the hybridising experiments go 

 to show that all the domesticated colour-varieties 

 have arisen from C. cutleri by loss-variation or 

 loss-mutation. It does not follow, however, that 

 wild species have arisen in this way, as some 

 believe, . for it is significant ' that the Brazilian 

 wild species, C, rufescens, yields sterile hybrid 

 males when crossed with the domesticated varie- 

 ties, while similar crosses between C. cutleri and 

 domesticated varieties yield completely fertile 

 hybrids. One of the general results of Prof. 

 Castle's hybridisation experiments is to confirm 

 his previous conclusion that size inheritance is 

 blending and does not mendelise. It is not 

 denied, however, that in special cases mendelising 

 factors may exist that affect size. 



In another study Mr. Sewall Wright deals with 

 the genetic factors determining coloration in 

 guinea-pigs and with the conditions which may 

 account for continuous series • of variations. 

 " Intermediates between varieties which men- 

 delise regularly have been found to follow very 

 definite modes of inheritance, which, however, 

 are very different in different cases, and could 

 not possibly be predicted a priori." He shows 

 that a complex of the most varied causes may 

 underlie an apparently simple continuous series 

 of variations. 



Of great interest, again, are the prolonged 

 breeding experiments that Prof. Castle has made 

 with hooded rats. It is shown that the factor for 

 hooded colour pattern may vary in genetic value. 

 There may be genotypic variation in grade as 

 well as ' phenotypic fluctuation — a conclusion 

 which brings us back to a familiar Darwinian 

 doctrine. "Racial changes," Prof. Castle writes, 

 " may be effected through selection by the isolation 

 of genetic fluctuations, as well as by the isola- 

 tion of mutations. Moreover, genetic fluctuation 

 makes possible progressive change in a particular 

 direction, repeated selection attaining results 

 which it would be quite hopeless to seek by any 

 other means." The study of the hooded rats, 

 previously reported on by Castle and Philipps in 

 1914, has been carried through three or four 

 additional generations. "The additional genera- 



i (i) "Studies of Inheritance in Guinea-pigs and Rats." Bv W. E. 

 C-istle and Sewall Wright. Pp. 192-1-7 plates. Carnegie Institution of 

 Washington, Publication No. 241 (1916). 



(2) " Gonadectomv in relation to the Secondarv Sexual Character": of 

 some Domestic Birds." By H. D. Goodale. Pp. 52-f7 plates, /it'd., 

 Publication No. 243 (1916). 



(3) "The Jukes in 1915." By A. H. Estabrook. Pp. vu-r85-|-26 charts. 

 /it'if , Publication No. 240 (1916). 



(4) "Fecundity 7'ersus Civilisation : A Contribution to the Study of Over- 

 population as the Cause of War and the Chief Obstacle to the Emancipation 

 of Women. With Especial Reference to Germany." By Ad«lyne More. 

 With an Introduction by Arnold Bennett. Pp. 52. (London : G. Allen anfi! 

 Unwin. I,td.. 1916.) Price 6rf. net. 



