August 9 1906] 



NATURE 



349 



Ij;- n-adily closed, a metal screen is hung down the 

 upper half of the tube at the back to provide an air 

 space at the top, to which the men can escape by an 

 air-lock through the screen on the occurrence of an 

 inrush of water, and pass out through an emergency 

 air-lock in the bulkhead behind. 



The author has collected together a large quantity 

 of information from a variety of publications, so as to 

 present a fairly complete record of the numerous sub- 

 aqueous tunnels carried out by means of a shield, 

 and more particularly those where compressed air 

 has been also resorted to, of which there are several 

 interesting examples in Great Britain, France, and 

 the United States, all constructed within the last 

 twenty years. The clear descriptions are very well 

 illustrated by numerous drawings; and the book de- 

 >crves a cordial welcome from all persons who are 

 <oncerned or interested in the latest developments of 

 •subaqueous tunnelling. 



I'KOBLEMS I.\ METABOLISM. 

 I'rohlews in Animal Metabolism. By J. B. Leathcs. 

 Pp. viii-l-205. (London : John Murray, igo6.) 

 Price 7s. 6d. net. 



THIS volume is the latest of the series that Mr. 

 .Murray is issuing in connection with the work 

 •of the physiological laboratory of the London Uni- 

 versity. The subject Dr. Leathes took for his lectures 

 IS perhaps the most important one in the whole of 

 ■chemical physiology. In a study of metabolism one 

 seeks to understand the innermost workings of the 

 living cells, and thus to comprehend the sum total 

 of the chemistry of life. In order, however, to pave 

 the way for such complete knowledge it is necessary 

 to study individual chemical reactions, the items that 

 go to form the final sum ; and so in the interesting 

 book Dr. Leathes has produced he is mainly con- 

 cirned with a separate consideration of the way in 

 which the carbohydrates, fats, and proteids are 

 iililised, and finally catabolised. 



The author has taken infinite pains to get his facts 

 correct, and has presented the subject in an extremely 

 clear way. He is able to point out quite lucidly how- 

 far present knowledge carries us, and where specula- 

 lion steps in to fill up the gaps. One becomes con- 

 scious of the width of these gaps when one realises 

 that any exact knowledge of how simple substances 

 like sugar are ultimately converted into water and 

 carbon dioxide in the body is at present lacking. In 

 the case of the more complex materials, such as the 

 proteids, hypotheses are still more numerous, because 

 our facts are still scantier. 



The whole work is full of pregnant suggestions, 

 ;uid the writing is so attractive that one can con- 

 fidently recommend it to all those who desire a picture 

 of exactly where physiology stands at the present 

 day in relation to these important matters. 



The spirit of the physiological chemist should not 

 be to make this branch of science an offshoot of 

 chemistr)', but to use organic chemistry as the means 

 to an end. This is the correct attitude that Dr. 

 Leathes assumes throughout. In the remote past 

 NO. 19 19, VOL. 74] 



so-called physiology was largely anatomy. When all 

 that anatomy could contribute had been learnt, it 

 was found that the real work of the physiologist was 

 only beginning. So, too, as Dr. Leathes points out, 

 we look forward to a future in which chemistry will 

 have contributed its share, and the workers will dis- 

 cover that physiology has still problems before it 

 which cannot be learnt from pure chemistry, any 

 more than the whole of physiology can be learnt by 

 dissections. 



The subject of proteid metabolism is in the air just 

 now, so it is specially interesting to ascertain what 

 views Dr. Leathes holds in relation to it. He accepts 

 the view which is daily gaining greater credence, that 

 in digestion the albuminous molecule is broken up 

 into quite simple substances, mainly of the amino- 

 acid variety. He believes that these are absorbed as 

 such, and that the work of proteid synthesis is carried 

 out by the living cells of the tissues from these 

 crystallisable products transported to them by the 

 blood and lymph. He admits this hypothesis is in the 

 unproven condition, but has himself been successful 

 in showing that the nitrogen of the blood, combined 

 in amino-acids and molecules of that order, is in- 

 creased during absorption. To identify the individual 

 amino-acids is a matter of much greater difficulty, and 

 a simple calculation shows how greatly even the most 

 abundant of them must be diluted by the whole mass 

 of the blood even during the progress of the absorp- 

 tion of a considerable meal. 



His views on the calabolism that proteids undergo 

 very largely coincide with those of Folin. The 

 nitrogen of ingested albumin is readily split off with 

 comparatively little loss of energy and discharged via 

 the liver as urea. The non-nitrogenous residue is 

 therefore available as a source of heat and energy in 

 much the same way as fat and carbohydrates are. 

 Until, therefore, we know how the cells dispose of 

 such simple organic compounds as fat, our knowledge 

 regarding the fate of the fat-like moiety of proteids 

 must be in abeyance. Dr. Leathes puts this much 

 more fully, but very clearly, which makes one wonder 

 why, in another part of the book, all his arguments 

 are against the possible origin of fat from proteid 

 intra-cellularly. 



Is it, then, advisable to limit our proteid intake 

 to the low level advocated so forcibly by Chittenden? 

 Should we take only sufficient to balance the small 

 amount of proteid waste that is associated with tissue 

 activity? In his answer to this question Dr. Leathes 

 has taken an independent and original line. He 

 admits that the necessary minimum is much less than 

 the conventional dietary of loo grams daily, but he 

 thinks it does not necessarily follow that it is un- 

 physiological to take more than the minimum, any 

 more than it is unphysiological to take any food 

 which yields more than the minimum of fsecal refuse. 

 In the infant, the dietary provided by nature in the 

 amount of milk it takes is, even after making due 

 allowance for growth, at least ten times greater than 

 the minimum. The minimum can therefore hardly 

 be normal for the adult ; and a possible reason for 

 this is that there mav be a few members of the amino- 



