REVIEWS 165 



to present chemical theory such a phenomenon is impossible. The book closes 

 with a suggestive discussion of asymmetric syntheses in nature. 



The book is well worth careful study, as much on account of the suggestive 

 discussion of those problems the solution of which is still incomplete, as for the 

 well-digested and complete summary of the work already done. When it is 

 remembered that English is a foreign language to the author, the diction must 

 be regarded as exceedingly good, but although two pages of errata are appended 

 these by no means include all the misprints which ought to be corrected in 

 a future edition. A. Scott. 



ZOOLOGY 



The Quantitative Method in Biology. By Julius MacLeod, Professor of 

 Botany in University of Ghent. [Pp. viii + 222.] (Manchester : at the 

 University Press ; London : Longmans, Green & Co. 1919. Price i$s. net). 

 THIS book, written by Professor MacLeod during his enforced absence from his 

 country, and published by Manchester University Press, is a valuable contribution 

 to the mathematical and quantitative aspect of modern biology. The author 

 writes well, ' and his thoughts are tersely expressed ; the book begins by the 

 demonstration of the underlying fact that the notion of species is a chemical notion, 

 and that though the number of organic substances known to science do not exist in 

 sufficient diversity to explain the occurrence of millions of animal and plant species, 

 the mixture of many of these substances in varying quantities in different species is 

 the explanation of the phenomenon of the multiplicity of animals and plants. 



Professor MacLeod distinguishes carefully between '' plasticity " of a species 

 such as found in Leontopodium alftinum when the alpine form becomes transformed 

 into the low altitude form, and between "complexity" such as is due to the 

 occurrence in one species of several distinct hereditary forms. The author 

 discusses the questions of variation under cultivation and in the state of nature, 

 and considers that the idea that variation is more common under cultivation than 

 in nature is not really true, and he gives examples in support of his claim. 



The author draws the attention of zoologists to the wide and as yet hardly 

 explored field of quantitative biology such as is offered to the embryologist and to 

 the systematist, in the development of legs, antennae, wings, etc. With regard to 

 the question of variation in embryology, the author draws attention to the fact that 

 observers are wont to call a piece of work, such as the examination of two tortoise 

 embryos, a '' Memoir on the Embryology of the Chelonidae," etc., and to base 

 their observations on too small a collection of material. Professor MacLeod 

 believes that the application of the quantitative method to embryology would 

 enable us to reduce the complicated notion of Development to terms of the simple 

 notion of growth of the Primordia (or simple properties). 



The last sections of this work are taken up by an explanation of the law of 

 probability in its application to the measurements of variable properties of animals 

 and plants. 



Owing to the concise and terse manner of writing and to its arrangement in 

 short paragraphs this book is not very readable ; but for consultation purposes the 

 arrangement is very convenient. 



Professor MacLeod is to be congratulated on having written a book which is 

 sure to be of use both to the expert and to the student. 



J. B. G. 



