December 9, 1922] 



NA TURE 



769 



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.'] 



Spectrum of the Night Sky. 



I have now succeeded in obtaining a spectrogram 

 showing the general features of the spectrum of the 

 night sky in the south of England, with the moon 

 below the horizon. The exposure given was about 

 50 hours, beginning each night not earlier than 

 z\ hour.-, after sunset, and closing about midnight. 

 There appears, therefore, to be no possibility that 

 sunlight or moonlight intervened. 



The spectrum shows the bright yellow-green 

 aurora line very strongly. There is a continuous 

 spectrum corresponding in distribution to the solar 

 spectrum, and showing the dark Fraunhofer lines 

 H and K. These are perfectly definite. The ex- 

 posure is not enough to show the other Fraunhofer 

 lines definitely, and, in any ease, the instrument used 

 is only capable of showing a few of the strongest of 

 them. 



There is no trace on this plate of the nitrogen 

 bands, which form so conspicuous a part of the 

 spectrum of the polar aurora. From some exposures 

 I have made in the neighbourhood of Newcastle, 

 three degrees farther north, I believe that the negative 

 bands of nitrogen are a normal feature of the night- 

 sky spectrum there. But more work is required 

 on this point. Rayleigh. 



Terling Place, Witham, Essex. 

 November 25. 



Medical Education. 



It is stated in Nature (November 18, p. 683) that 

 " The professional course has grown so full in the 

 training of a medical student that it has become 

 increasingly difficult to cover the ground and secure 

 qualification in a reasonable time." It seems that 

 chemistry and physics are to be placed outside the 

 professional curriculum, but biology is to be retained. 

 A knowledge of chemistry and physics is necessary 

 to the doctor ; and much of the recent advance in 

 both medicine and surgery is due to discovery in 

 these sciences. But can any one tell us of what 

 utility, practical or intellectual, is the biology which 

 medical students learn — facts about the classification 

 of plants, the vascular system of the sea-urchin, the 

 digestive system of the leech, the bones in the cod's 

 head, and so on ? No one is a better physician or 

 surgeon for such knowledge ; and, therefore, since 

 it has no bearing on later study and practice, it 

 is forgotten as soon as the prescribed examinations 

 are passed. 



For the medical man the intellectual value of 

 biology should lie, if anywhere, in interpretation. 

 It should cause him to think. He should learn man's 

 place in Nature — how he resembles and differs from 

 other living beings, and how these likenesses and 

 differences arose. Man is in bodv and mind above 

 all the educable, the trainable, the adaptive being. 

 From birth forwards he develops mainly in response 

 to use. He is rational and intellectual because his 

 mind grows through functional activity. That is his 

 special distinction ; that places him in Nature. The 

 medical student learns nothing of all this. He may 

 be taught, incidentally as it were, that some characters 

 are inborn, or acquired, or inheritable. But a year 



or so later, physiologists and pathologists tell him 

 the quite indisputable truth that every character 

 takes origin in germinal potentiality (predisposition, 

 diathesis), and arises in response to some sort of 

 nurture — i.e. that every character is equally innate, 

 acquired, and inheritable. If the student thinks at 

 all, he must conclude, as Prof. Armstrong says very 

 truly in another connexion (Nature November 11, 

 p. 648), " We are mouldering away in our laboratories 

 and when we seek to make known what we have been 

 doing we use a jargon which wc cannot ourselves 

 understand." 



The medical student may be told that Natural 

 Selection is an interesting speculation, but that no 

 man has seen it in operation. Again, if he thinks, 

 he will conclude that, owing to defective opportunities 

 for observation, no man could see Natural Selection 

 in operation among the wild animals and plants 

 which biologists study. Nevertheless, a year or two 

 later he will perceive it in full swing in the case of 

 tuberculosis and every other lethal and prevalent 

 human disease, and will learn that every human race 

 is resistant to every human disease precisely in 

 proportion to the length and severity of its past 

 experience of that disease. There are scores of 

 diseases and hundreds of races and sub-races of man- 

 kind ; and, therefore, in some thousands of instances 

 — whenever and wherever close observation is possible 

 — he will find Natural Selection causing adaptive 

 evolution. Moreover, he will learn that just as 

 human races alter gradually in powers of resistance, 

 so, at the other end of the scale, bacterial races alter 

 in virulence when removed from one kind of animal 

 to another, a thing quite inexplicable except on 

 grounds of Natural Selection. 



The student may be taught that effective selection 

 occurs among mutations, not fluctuations. A year 

 or so later he will perceive tuberculosis selecting amid 

 all shades of difference, with the result that races 

 present all shades of evolution. He may be taught 

 that mutations segregate and that their inheritance 

 is alternate. A year or so later he will learn that 

 human mutations (e.g. idiocy, hare-lip, club-foot) are 

 inherited, perhaps for many generations, in a patent 

 or latent condition, and that only their reproduction 

 is alternate. Moreover, he will wonder, if mutations 

 segregate, how it happens that long - lost ancestral 

 traits sometimes reappear in purely bred domesticated 

 varieties (e.g. pigeon, poultry, and many plants). 

 He may be taught that evolution depends on mutations 

 and that mutations do not blend. A year or two later 

 he will learn that human races never differentiate 

 while there is inter-breeding, but diverge rapidly and 

 infallibly when separated by time and space ; that, 

 though men are fond of telling about wonders, yet 

 in the whole of written human history (4000 years 

 or more) no useful human mutation has been recorded, 

 nor one that changed the type of a race ; that all 

 human varieties (e.g. negro and white), like all 

 natural varieties (e.g. brown and polar bear), blend 

 perfectly when crossed in all characters except those 

 linked with sex; and, lastly, that "lost" ancestral 

 traits never reappear except when one of the parties 



to 1 1: ss i- derived from a domesticated variety. 



If he thinks at all, lie will conclude that Natural 

 Selection is founded on fluctuations, but that man, 

 as Darwin noted, " often begins his selection by some 

 half-monstrous form, or at least by some modification 

 prominent enough to catch the eye or to be plainly 

 useful in him." He may be taught that the doctrine 

 of recapitulation is doubtful. But if he thinks at all, 

 he will perceive lh.it any other mode of evolution 

 ami development 1^ totally inconceh able. And so on. 



The point I wish to emphasise is that medical 

 men, with an acquaintance with man infinitely more 



NO. 2771, VOL. I IO] 



