i6f 



NATURE 



[May I, 1919 



Prof. Loeb is an out-and-out "mechanist," as 

 we all know. He is impatient (as he tells us in 

 the first words of his preface) with "the attempts 

 of vitalists to show the inadequacy of physical 

 laws for the explanation of life." He insists on 

 the "quantitative methods of the physicist," and 

 will have nothing- to say to the romantic, or 

 anthropomorphic, tales of "scientific popularism." 

 His book begins with an account of the sym- 

 metry of the organism, as the starting-point for 

 his theories of conduct ; that is to say, he finds in 

 the existence of bodily symmetry, whether radial 

 or bilateral, a simplification of all further analysis. 

 The symmetry is a dynamical as well as a mor- 

 pholog-ical one ; there is a symmetry which corre- 

 sponds with the impulses from without, as to the 

 reactions from within ; muscular system and 

 nervous system have their own corresponding sym- 

 metries, and the whole problem of action and 

 reaction is simplified thereby. But it does not 

 follow that all animals are symmetrical — at least, 

 in this simple fashion. The spiral Euglena, for 

 instance, is a harder case; and the experimentalist 

 may convert the symmetrical into an unsym- 

 metrical animal, as when he destroys one hemi- 

 sphere of a dog's brain, or makes a beetle blind 

 of one eye. The "reflex actions" of the physio- 

 logist are the reactions of parts, or isolated seg-- 

 ments ; a similar or analogous reaction of the 

 whole is likewise assumed to be, or may be inter- 

 preted as, a phenomenon of a purely physico- 

 chemical nature. And these reactions of the whole 

 organism are what Prof. Loeb calls "tropisms. " 



Throug-h such reactions, or tropisms, Prof. Loeb 

 leads us, in connection with the various stimuli 

 of light, heat, electricity, chemical action, gravity, 

 contact, and so forth, and at last comes face to 

 face with the more recondite themes of instinct 

 and memory. Let us consider a single experiment 

 out of the great number which this small book 

 relates. Many animals, very humble ones in- 

 cluded, tend to move towards the light, while 

 some, on the other hand, retire into the darkness 

 or the shade ; some love the light, and some hate 

 and avoid it, as we are apt, in our anthropo- 

 morphic fashion, to say. Suppose, now, that we 

 illuminate the two eyes of a fly by separate beams 

 of light, of equal intensity and similarly directed. 

 The fly will not choose between the two lights, 

 says Prof. Loeb, as a belated traveller might choose 

 between the lights of two village inns ; it will do 

 something- much simpler, and apparently more 

 mechanical. It will travel straight along a line 

 perpendicular to that which joins the two lights ; 

 it will follow the resultant of the two stimuli. Not 

 only so, but if we alter the direction of the beams, 

 or cause them to differ in intensity, so that in 

 either case one eye receives more illumination, 

 more "phototropic stimulus," than the other, then 

 the creature will move along- a perfectly definite 

 line, which can still be simply calculated as the 

 resultant of the two forces involved. The experi- 

 ment is an ingenious and an elegant one, and, 

 without for a moment doubting the results which 

 Prof. Loeb and his pupils have repeatedly 

 NO. 2583, VOL. 103] 



obtained, we can honestly say that we should 

 dearly like to see it performed. 



We dare not attempt to discuss the great philo- 

 sophic questions that are involved in the whole 

 course of these experiments. We have a notion 

 that "anthropomorphism " is not got rid of quite 

 so easily, however much we change our phraseo- 

 logy, as Prof. Loeb would have us believe, and 

 that, great as are the lessons of mechanics, they 

 do not tell the whole story, after all. Be that as 

 it may, the element of precision, the quantitative 

 element, the strict, experimental method, is con- 

 spicuous in Prof. Loeb's work, and our knowledge 

 is manifestly increased thereby. I think it was 

 Liebigf who said, in one of his letters to Faraday, 

 that (in those days) a man might be an eminent 

 g-eologist in England who knew nothing of 

 physics, nothing of chemistry, nothing- even of 

 mineralogy. Change the wording, and the bio- 

 logist may (or once upon a time might) have 

 begun to feel uneasy. It is something to be 

 taught or reminded by Prof. Loeb, and by the 

 whole brotherhood of experimental biologists, that 

 the naturalist cannot live alone, but works in a 

 field inextricably connected, for better for worse, 

 with the whole range of the physical sciences. 



Prof. Loeb has a boundless wealth of ideas. In 

 this book and in his other books and papers we 

 seem to see them tumbling- one over another. He 

 has enoug^h and to spare for all his pupils and 

 fellow-workers, so that all who come to him may 

 eat and be filled. Moreover, his manifold experi- 

 ments all have the hall-mark of simplicity, and 

 this is surely one of the greatest things that can 

 be said of any experimenter. There is no parade 

 of elaborate apparatus, nor does it ever seem to 

 be required. Simplex si^iUutn veri ! 



The book concludes with a bibliographical list 

 of nearly six hundred titles — a catalogue of books 

 and papers on experimental biolog-y, in the sense 

 in which Prof. Loeb himself deals with it. In the 

 first hundred and fifty titles (and I hav^ gone no 

 further in my analysis) sixty-three are German, 

 forty-three American, thirty-eight French, and 

 four more are Dutch or Italian. I shrink from 

 doing- the addition and subtraction which would 

 reveal our British share. 



D'Arcy W. Thompson. 



OUR BOOKSHELF. 

 The Strawberry in North America. History, 



Origin, Botany, and Breeding. By Prof. S. W. 



Fletcher. Pp. xiv + 234. (New York: The 



Macmillan Co. ; London : Macmillan and 



Co., Ltd., 1917.) Price 85. net. 

 With marked success Prof. Fletcher has gathered 

 into a comprehensive survey much information of 

 great interest in the history and development of 

 the strawberry. Though the book is primarily 

 written for American readers, it appeals to the 

 Eng^lish gardener and student of horticulture, as 

 English varieties and methods of cultivation had 

 a strong influence on the improvement of the fruit 

 in North America. Garden cultivation began 



