May 2, 19 1 8] 



NATURE 



163 



essential parts of the Claude and Linde air lique- 

 fiers and the principles underlying- their working. 

 The Hampson liquefier is not described. The 

 fractionation of liquid air is illustrated by diagram- 

 matic representations of Linde's and Claude's frac- 

 tionating- plants, and the merits of the two sys- 

 tems are compared. 



The theory of refrigeration is dealt with from 

 the thermodynamic point of view, and a considera- 

 tion of the expansion of gases against external 

 pressure and without external pressure leads up 

 to the behaviour of the working substance in a 

 refrigerating- machine. A comparison of ideal 

 indicator diagrams of the cycle with those obtained 

 in practice is utilised to bring- out the points need- 

 ing careful attention in work of this nature. The 

 construction of the essential parts of refrigerating 

 machines is described in some detail, and pro- 

 fusely illustrated with excellent reproductions. 

 The book concludes with a chapter on the applica- 

 tions of refrigeration to ice-production, cold stor- 

 age, and the preservation of foodstuffs, and a 

 description is given of the construction of railway 

 wagons and steamships designed for the transport 

 of perishable foodstuffs. 



On the whole, the subject-matter of the book is 

 well thought out and presented to the reader in 

 logical sequence and in a very lucid and readable 

 form. The illustrations are numerous, well repro- 

 duced and explained, and deserve a special word 

 of commendation. The bibliography in the second 

 part of the book is fairly comprehensive, but the 

 value of the first part might, perhaps, be enhanced 

 by a little further attention to this point. 



The utility of the book would be increased by 

 the addition of an index. 



A. G. G. Leonard. 



THE NERVOUS IMPULSE. 



The Conduction of the Nervous Impulse. By Dr. 

 Keith Lucas. Revised by E. D. Adrian. Pp. 

 xi+io2. (Monographs of Physiology.) (Lon- 

 don: Longmans, Green, and Co., 1917-) Price 

 55. net. 



IN the spring of 1914 Keith Lucas by good 

 fortune was called upon to deliver the Page 

 May memorial lectures at University College, 

 London. He intended to rewrite the lectures for 

 the present monograph, and by July, 1914, had 

 completed eleven of the thirteen chapters. At the 

 outbreak of war he offered his services to the 

 country, and was posted to the Royal Aircraft 

 Factory at Farnborough, where, until he was 

 killed in an aeroplane accident on October 5, 1916, 

 he was fully occupied with problems of flying. 

 The two missing chapters have been written by 

 Mr. Adrian, pupil and fellow-worker, for the most 

 part from the lecture notes. 



Nearly one hundred years of intensive investi- 

 gation has been devoted to the nervous impulse. 

 The volume of the work and the number of 

 workers of outstanding ability who have engaged 

 in attempts to discover the nature of a wave 

 NO. 2531, VOL. lOl] 



probably of no great intrinsic complexity miy 

 appear strange to a physicist. The reason is one 

 of scale : the single conducting unit, the nerve- 

 fibre, being only some 18 to 20 /x in diameter, i\ 

 too delicate for separate treatment. It is neces- 

 sary, therefore, to work with the nerve, which 

 is a bundle of many hundreds of fibres. For this 

 reason so simple a matter as the relation between 

 the intensity of the stimulus and the amplitude of 

 the wave is incapable of direct measurement, for 

 it is impossible to determine directly whether an 

 increase in the integral response of the nerve is 

 due to an increase of the response of individual 

 fibres or to an increase in the number of fibres 

 called into action. 



Owing to this ineradicable difficulty, the whole 

 structure of our knowledge of the nervous impulse 

 is based upon an assumption, namely, that the 

 molecular wave suffers a decrement in traversing- 

 a region the conductivity of which has been im- 

 paired by some narcotic such as the vapour of 

 alcohol, and that the capacity of the wave for 

 traversing a narcotised region is a measure of its 

 amplitude. The effect of this fundamental in- 

 security is, to quote Lucas's words, that "the 

 argument of the experiments becomes somewhat 

 complex. . . . The experiments are often easily 

 made, even with a considerable degree of 

 accuracy ; it is in their interpretation that the real 

 difficulty begins. And this difficulty arises again 

 and again from the same cause, that nerves and 

 muscles are not units, but each composed of many 

 fibres." 



What is the nature of the wave? It is accom- 

 panied by a change of electric potential, but 

 as the rate of travel is only of the order of 

 40 ft. per sec, it cannot be a simple electrical 

 wave. It is true that on Kelvin's cable theory 

 and by making many assumptions it can be shown 

 that a wave of simple displacement of electricity 

 would travel in a structure like the nerve-fibre at 

 a speed of this order. But by delicate micro- 

 chemical technique it has been found possible to 

 detect an increased output of carbon dioxide 

 during^ the passage of the wave, and a rise of 

 temperature has been measured of the order of 

 7 X 10-^ of a degree Centigrade, not to be accounted 

 for save as heat liberated during the passage of 

 the wave, which would therefore appear to be 

 i one of exothermic chemical change. 

 ! These and other cognate problems are discussed 

 in the clear logical way so characteristic of Lucas's 

 mind, and from these relatively simple issues the 

 author proceeds to consider how far the pheno- 

 mena of the isolated nerve may be used to inter- 

 pret the much more complex phenomena of the 

 central nervous system. 



I commend the book to physicists — to the 

 physiologist it is a matter of professional interest, 

 but to the physicist it should come as a romance. 



Of the gifted author himself there is no space 

 to speak. His skill, his courage, his clear vision 

 are fittingly dwelt upon in a prefatory note by 

 Prof. Starling which could not he bettered. 



W. B. Hardy. 



