May 19, 1921J 



NATURE 



357 



vidual workers with one another and with the 

 results attained in the most exact researches. 

 This leads up to a consideration of the con- 

 clusions that can be drawn from the work, or of 

 the additional experiments that must be made 

 before any conclusions can be drawn. 



It is to be feared that those teachers who most 

 need the stimulus and the criticisms of this book 

 will be the last to read it; but many young-er 

 teachers, who have already tasted of the tree of 

 knowledg-e, will find in the book fresh inspira- 

 tion for the study of chemical discovery, and 

 guidance as to its application in the daily routine 

 of the school. T. M. L. 



Cocoa and Chocolate. 



Cocoa and Chocolate : Their History from Planta- 

 tion to Consumer, by Arthur W. Knapp. 

 Pp. xii + 2io. (London: Chapman and Hall, 

 Ltd., 1920.) I2S. 6d. net. 



MR. A. B. WALKLEY has recently explained 

 in his inimitable fashion how the whole 

 future of the drama and dramatic art in England 

 depends on the withdrawal of the rule that choco- 

 lates must not be sold in theatres after 8 p.m. 

 A commodity which has such a profound, if 

 indirect, influence on an Important phase of 

 English culture merits serious treatment, and it 

 was clearly time that the history of cocoa and 

 chocolate should be written, and written in a 

 popular fashion. 



When, about 1735, Linnaeus coined for the 

 cacao tree the picturesque name of Theohroma 

 cacao, the English chocolate-making industry had 

 been in existence about seven years. It made 

 slow progress in its early days, and 100 years after 

 its inception the imports of cacao beans amounted 

 to only 450 tons per annum. Since then, and 

 especially in the last ten years, the rise has been 

 remarkable, the imports of the raw material for 

 home consumption in 1919 being over 64,000 

 tons. In addition, there are considerable imports 

 of foreign-made cocoa and chocolate. The 

 chocolate-maker has, therefore, no reason to 

 complain of the descent of chocolate from its lofty 

 estate as a food of the "gods" to the more 

 humble condition of the flapper's confection. 



Mr. Knapp is connected with an enterprise 

 which not only makes everything that can be 

 made from cacao beans, but also owns plantations 

 of cacao trees. He has had, therefore, unique 

 opportunities of making himself acquainted with 

 every branch of the industry, and he has clearly 

 not only utilised these opportunities to the full, 

 but also has thought to some purpose about the 

 NO. 2690, VOL. 107] 



numerous unsolved problems connected with 

 cacao-planting and the preparation of the beans 

 for the market. There must be few planters 

 whose ideas on the shading of cacao trees, the 

 fermentation of the beans and the characteristics 

 of a good cacao will not be clarified by a perusal 

 of Mr. Knapp 's pages. 



Though chocolate is regarded by the ordinary 

 person as a luxury, it has always had a band of 

 devotees, who regard it as an important food-- 

 stuff. Mr, Knapp is one of these enthusiasts, and 

 he provides the inevitable table, comparing the 

 " fuel value " of chocolate with those of some 

 ordinary foods. He omits, however, all reference 

 to price per calorie, which would bring out the 

 interesting fact that even plain chocolate is an 

 expensive food, and that when consumed in the 

 form of those super-confections which, if one may 

 judge from the contents of chocolate-shop 

 windows, constitute the bulk of the chocolate 

 consumed to-day, it is a very expensive food— 

 in fact, as the plain man believes, a luxury. 

 The author of so interesting a book as this may, 

 however, be forgiven a trifling obsession of this 

 kind. It is a book which should be in the hands 

 of all officials of tropical agricultural depart- 

 ments (for whose experimental work Mr. Knapp 

 expresses much admiration) and of all cacao 

 planters, and it is so siijiply and clearly written 

 that it might even be read by the chocolate con- 

 sumer if there were in this country any adequate 

 machinery for making the existence of interest- 

 ing technical literature known to the general 

 public. The illustrations are numerous, good 

 and well selected. T. A. H. 



Our Bookshelf. 



An Introduction to Combinatory Analysis. By 

 Major P. A. MacMahon. Pp. .viii-t-71. (Cam- 

 bridge : At the University Press, 1920.) 

 75. 6d. net. 



In this little book Major P. A. MacMahon has 

 given a short introduction to his two volumes on 

 combinatory analysis which were published in 

 19 1 5- 16. The theories of combination, permu- 

 tation, arrangement, order, and distribution which 

 are dealt with in those volumes present technical 

 difficulties ; it is, therefore, a great advantage 

 that such an introduction should exist, for the 

 gradual development of the subject by easy stages 

 will prove interesting to the reader and whet his 

 appetite for the larg-er tomes which await him. 



In the first chapter the elementary theory of 

 symmetric functions is introduced, and on it the 

 theory of distributions is afterwards based. The 

 author treats in turn the simplest problems of 

 the distribution of objects into boxes, one object 



