1 64 



NATURE 



[August 4, 1923 



proves conclusively that the defect is not due to a 

 diminution of a hypothetical red sensation, because 

 all the rays coming through the blue-green glass are 

 supposed to atfect the red sensation, and yet we have 

 been able to correct the erroneous match by the 

 subtraction of red light." 



Now the question of a longer or shorter spectrum 

 with otherwise absolutely normal vision is one which 

 can be dealt with equally easily by all theories. To 

 show the power of the Young-Helmholtz theory, I 

 shall take the most extreme case possible, that in 

 which the peculiarity amounts to clichroma.sy. Let 

 the pink and violet colours be represented by 

 ;riR4->'iG-f^iB and x^\.-\-yfi-^z^ respectively, in 

 the usual trichromatic notation ; and let the colour 

 abstracted by the blue-green glass be aiR+6iG4-c,B 

 in the case of the pink, and a^^h^jArC^ in the 

 case of the violet. So the colours seen by the normal 

 eye are {x^ - a^JR + (^i - fti)G -f (2j - Ci) J3 and [x^ - a^ 

 R -f {y^ - 62)0 -t- {z^ - C2)B respectively. If these appear 

 to be identical, we have x-^- x.^=a-i^- a^, yi-y^^ 

 bi - b.^, Zi -Z2=Ci- Cj. These are the relations which 

 must'subsist amongst the unifiable colours and the 

 colours absorbed by the unifying medium. Now let 

 the dichromasy correspond to the condition ?R + 

 7;G-t-fB=0. The pink and violet are then express- 

 ible as {xi -Zi ^/f)R + (>'i -2i 77/f)G and {x^ -^2^/.<')R + 

 (^2 -■2'2'?/f)G respectively. These being identical, we 

 have (Xi - x^) : {yi -y-z) : {zi -Z2) =^ :v- 1, which are the 

 conditions for Dr. Edrige-Green's case. The tri- 

 chromatic theory, so far from being helpless, as he 

 asserts, not merely accounts generally for the 

 phenomenon, but tells quantitatively as well as 

 qualitatively what is happening. W. Peddie. 



Distribution of Megalithic Monuments. 



Mr. O. G. S. Crawford, in Nature of May 5, 

 p. 602, criticises what he terms my " speculations " 

 concerning the distribution of megalithic monuments 

 in England and Wales. I am sorry that apparently 

 he did not trouble to read the paper, and to see 

 exactly what I had to say on the matter. My aim 

 was to urge that there is a connexion, in England 

 and Wales, between the distribution of megaliths 

 and certain geological formations, the Granite in 

 Devon and Cornwall, the Chalk in Dorset and Wilts, 

 the Lias in Gloucester and Oxford, and so forth. In 

 this I found that I had been anticipated in part by 

 Mr. Crawford himself. Where we differ, of course, is 

 in the interpretation of the evidence. 



An examination of the paper will show Mr. Crawford 

 that I am well aware of the difl&culties involved in 

 the theory that the builders of megalithic monuments 

 were attracted to this country by the stores of gold, 

 copper, lead, and so forth, that it contained, and 

 that I discussed the very points to which he directs 

 attention. It must never be forgotten, however, 

 that megaliths are found in all parts of the world, 

 and that possibly the explanation of the presence 

 of these monuments in one country may serve to 

 explain their presence elsewhere. All I have done 

 is to put forward the theory, based on evidence 

 from all parts of the world, that the megalithic 

 civilisation of western Europe was derived from a 

 metal-using civilisation in the Ancient East. 



The attention of all who are interested in the 

 matter is being directed to the excellent work now 

 being done by Mr. Crawford at Southampton, and 

 we are all eagerly expecting the publication of the 

 fresh distribution maps of megalithic monuments 

 that Mr. Crawford promises us. But, admirable as 

 such work is, the final solution of the problems 

 presented by these monuments may, after all, come 



NO. 2805, VOL. 112] 



from a wide survey of facts derived from all parts 

 of the world, and not necessarily from detailed work 

 in a limited part of the field. W. J. Perry. 



The University, Manchester. 



The Concentration of Haemoglobin in Blood 

 Corpuscles. 



I HAVE very little doubt that Dr. Gorter is right in 

 suspecting that the method which is commonly used 

 for determining the volume of the red blood corpuscles 

 by centrifugalisation is not trustworthy (Nature, 

 June 23, p. 845). Whether the red corpuscles are 

 biconcave discs or hollowed cones, or indeed, whatever 

 their shape may be, they cannot be packed together 

 without leaving spaces between them unless they are 

 deformed : and if they are deformed there is every 

 reason to be suspicious about their water content 

 remaining unaltered. 



The usual method is to centrifuge the blood until 

 the volume of the cells ceases to become smaller, the 

 apparatus generally making 3000 to 5000 revolutions 

 a minute with a disc of something less than a foot. 

 It is easy to convince oneself that the final result 

 depends on just how the process is carried out, for 

 it is different if the blood is first gently centrifuged, 

 say at about 2000 revolutions, and then exposed to 

 the full speed, from what it is if the high speed is 

 used from the beginning. So dependent is the figure 

 obtained on the precise details of the method that, if 

 real comparisons between different bloods is required, 

 it seems to be essential that they must be in the 

 centrifuge simultaneously. 



The method seems never to have been examined 

 critically. What is wanted is a comparison between 

 it and the results calculated from the concentrations 

 in whole blood and in plasma of some substance 

 present in plasma and not in red corpuscles, which 

 can be estimated with a high degree of accuracy. 

 Without some control of this kind the method must, 

 for absolute values at any rate, remain under suspicion. 



A. E. Boycott. 

 Medical School, 



University College Hospital, W.C. 



Effect of Plant Extracts on Blood Sugar. 



Our studies in connexion with insulin led us to 

 the conception that carbohydrate metabolism is 

 performed by an oxidising ferment mechanism. This 

 theoretical conception induced us to test vegetable 

 material, known to contain oxidases and peroxidases, 

 for oxidising substances having an insulin-like action. 

 In December 1922 we injected 5 c.c. of juice from a 

 new potato intravenously into a 1500 gm. rabbit and 

 noted a fall of blood sugar in one hour from 0-17 to 

 0-13 per cent. Since then we have found that sterile 

 pieces of raw potato, and juice expressed from these, 

 introduced into a glucose solution, after incubation 

 for twenty-four hours at 37° C, caused this to lose 

 from 26 to 36 mg. of glucose per 100 c.c. These 

 results were published in the Jour. Amer. Med. 

 Assoc, June 2, together with results indicating a 

 diminished glycolytic power of blood from diabetics. 



Winter and Smith published a note in the Journ. 

 Physiol. 57, 40 (Nos. 3 and 4), 19^2, which reached 

 the United States in April last, and in Nature of 

 March 10, p. 327, stating that they had obtained an 

 insulin-like substance from \^east. 



Collip, in Nature of April 28, p. 571, states that 

 he, working independently, found an insulin-like 

 substance in various vegetables, in yeast, and in 

 clams. Colhp's studies on insulin are of inestimable 



