August ri, 1923] 



NA rURE 



197 



difficulty of arranging for such a vertical line to appear 

 in the photograph would appear to be considerable. 

 Ropes suspended from small balloons are liable to be 

 deflected from the vertical by local air movements^ 

 and the system would involve additional apparatus. 

 The suggestion is an ingenious one, however, and 

 deserves to be tried. 



It should be noted, in conclusion, that recent ^ experi- 

 ments by Prof. Melvill Jones and Maj. J. C. Griffiths 

 have shown that it is possible to fly on such an even 

 keel that the photographic plate shall seldom be inclined 

 to the horizontal as much as 2°. This would result in 

 linear errors, on the uncorrected photograph, of less 

 than 1 1 per cent. In many cases this class of plotting 

 error can be permitted for detail, and in such cases no 

 knowledge of, or correction for, tilt would be required, 

 and all that would be necessary would be to know 

 the length of one line on the ground to give the scale. 

 There would be a great saving of time and expense 

 in plotting the map and in fixing ground points, and, 

 for the more rapid kinds of reconnaissance, in flat or 

 undulating country, progress may be hoped for in 

 this direction. 



Light and Health, 



Heliotherapy. By Dr. A. Rollier. With the Collabora- 

 tion of Dr. A. Rosselet, Dr. H. J. Schmid, Dr. E. 

 Amstad. (Oxford Medical Publications.) Pp. xxii + 

 288. (London : Henry Frowde and Hodder and 

 Stoughton, 1923.) 255. net. 



ALTHOUGH it has long been known that certain 

 radiations have a powerful action on physio- 

 logical processes, it is only in recent years that much 

 attention has been given to the subject as it affects 

 the higher animals. Apart from the mechanism of 

 carbon assimilation in the green plant, our eyes have 

 been mainly directed to the lethal effects of ultra- 

 violet rays, and, more recently still, to those of X-rays 

 and of radium. The author of the book before us was 

 one of the first to appreciate and to make practical 

 use of the beneficial action of sunlight. Dr. Rollier's 

 work at Leysin has been made familiar to readers of 

 Nature by the recent lecture given at the Royal 

 Institution by Dr. Saleeby, and the reviewer cannot do 

 better than refer those who wish for further information, 

 with abundant and deeply interesting illustrations, to 

 this translation of Dr. Rollier's book. Forewords are 

 contributed by Sir Henry Gauvain and Dr. Saleeby, 

 while special chapters are included on the scientific 

 basis by Dr. Rosselet, on the use of X-rays in the 

 control of the progress of the treatment by Dr. Schmid, 

 and on the adjuvants of heliotherapy by Dr. Amstad, 

 who also adds a chapter on non-tuberculous diseases, 



1 See Nature, May 26 and June 2, 1923. 

 NO, 2806, VOL. 112] 



The book itself is a most fascinating one and will 

 be found full of interesting details, not merely of 

 clinical nature, but of value to the student of science,, 

 art or morals. It should have a wide circulation, and 

 the only criticism that I am inclined to make is that 

 the price seems rather high. I refer to this now in 

 order not to end on a discordant note. It is difficult 

 to see what might be the cause of this high cost, and it 

 is to be feared that it may tend to restrict the sale of 

 a book which should be in the hands of everyone wha 

 has at heart the happiness of his fellow-men, and 

 especially of those who love children. I wish par- 

 ticularly to direct attention to the wide general interest 

 of the contents, because the title might give the 

 mistaken impression that it is a purely medical work. 



The scientific reader will notice that we have much 

 to learn as to the physiological action of light, and it 

 will probably serve the best purpose if I devote the 

 space available to a brief reference to the facts brought 

 out by Dr. Rollier's work and to the gaps which await 

 the results of further investigation, much of which can 

 be done in the laboratory. 



In the first place, we must distinguish between the 

 effects of rays of different wave-lengths. In rickets, 

 it is a limited region of the ultra-violet that is effective; 

 in tuberculosis, we have no precise knowledge of the 

 important region, except that the' heat rays of long 

 wave-length have to be guarded against. The necessary 

 exposure cannot be tolerated except under the cooling 

 influence of alpine air or of sea-bathing. Recent work 

 tends to show that the rays of the red end of the 

 spectrum may neutralise the benefit of the shorter 

 wave-lengths. There is scope for investigation of the 

 action of optical sensitisers, when atmospheric con- 

 ditions cut off the active rays. The red algge give 

 us an example to follow. It is also clear that exact 

 measurements and records are needed of the rays of 

 various wave-lengths present in the sun's light in 

 different places and at different times of the year and 

 day. 



Next, we may note that Dr. Rollier has from the 

 first been aware of the fact that the direct action of 

 the rays on a diseased organ is not what is required. 

 Exposure of the skin in any situation suffices. It is 

 natural to draw the conclusion that some photo- 

 chemical product is sent from the skin into the 

 circulating blood. But we have as yet no actual proof 

 of this, and there are other possibilities which cannot 

 be entered into here. In any case, we are shown that 

 the skin has some important functions hitherto un- 

 appreciated. 



Then there is the remarkable fact that it is only 

 those individuals whose skin takes on the well-known 

 brown pigmentation after exposure to the sun who 



F 1 



