314 



NATURE 



[February 2, 1893 



with. In the meantime colleges and schools must prepare 

 competent instructors for the work, and for both teacher 

 and taught this book is an admirable starting-point. In 

 it the whole field of small industries is well covered, and 

 the language is clearly expressed and well chosen. As an 

 example of the author's treatment we find under manures 

 (p. 49) :- 



" The land must be regarded by the planter as a bank in 

 which he has opened an account. If he continually draw 

 cheques on the bank, and make no fresh deposit to meet 

 the drain, he will sooner or later come to the end of his 

 capital, and the same argument applies to the soil. In 

 cacao and coffee cultivation in the West Indies, particu- 

 larly, on lands of peasant proprietors, one often sees the 

 planter take away crops year after year, whilst he does 

 next to nothing to make up for the heavy drain on the 

 land ; and then, after a time he finds he gets very small 

 crops, and he thinks the fault lies with the trees, or that 

 the soil is not adapted to the cultivation, whereas the 

 fault is entirely his own, as he has gone on taking away 

 from the soil without putting anything back." Again, "the 

 great fault hitherto committed by tropical planters has 

 been the confining of their attention to one kind of cul- 

 tivation on their land. If several different crops were 

 taken off alternately, as in a system of rotation, or grown 

 in different parts of the land, where the soil and climate 

 prove suitable, the planter would be in a much better 

 position than he is now, for he would not ' have all his 

 eggs in one basket.' " 



It is noticed that the valuable services rendered to 

 colonial industries by Kew and by the various botanical in- 

 stitutions in correspondence with Kew are fully recognised. 

 Further, the dedication of this first Text-book of Tropical 

 Agriculture to Sir Joseph Hooker is a compliment not 

 only to his own distinguished services, but also to those 

 of his father, for both in their day took the deepest in- 

 terest in the West Indies. It must be gratifying to the 

 late Director of Kew to learn " in the quiet of his retire- 

 ment that the influence of his work lives on and bears 

 fruit even in the far-away field " of the West Indies. 



D. M. 



CELLS 



THEIR STRUCTURE AND 

 FUNCTIONS. 



Die Zelle und Die G ewe be, GrundzUge der allgemeinen 

 Anatomie und Physiologie. Von Prof. Dr. Oscar 

 Hertwig. (Jena: Gustav Fischer, 1892.) 

 ' I "EXT-BOOKS on Histology introduce the structure of 



J- the tissues to their readers by a chapter on cells, 

 and the best treatises on Anatomy, either human or com- 

 parative, usually devote some pages to the consideration 

 of these, the most elementary of all the tissues. As so 

 many important advances have been made of late years 

 in our knowledge of the structure of cells and their con- 

 tained nuclei, of the properties of protoplasm, of the 

 division of nuclei and the part played by the nucleus in 

 cell multiplication, and of the influence exercised by cells 

 in the problems of hereditary transmission, the time has 

 obviously arrived for the production of a treatise devoted 

 to the description of the cell in its various aspects, obser- 

 vational as well as speculative. No better expositor of 

 the subject in all its bearings could be found than Prof. 

 Oscar Hertwig; who has himself conducted important 



investigations on this branch of anatomy. The book now 

 NO, 12 14, VOL. 47] 



before us treats of the general anatomy and physiology 

 of cells, and is to be followed by a second volume, in whicb 

 the origin and physiological properties of the tissues are to- 

 be expounded, as well as their structure. 



After a sketch of the history of the cell theory and of 

 the theory of protoplasm, in which, as is too often the 

 case in German text-books, the names of British ob- 

 servers and authors are conspicuous by their absence, he 

 defines a cell to be a little clump of protoplasm which 

 incloses a specially-formed constituent, the nucleus ; a 

 definition which accords with those previously made by 

 Leydig and Max Schultze. He then describes at con- 

 siderable length the characters of protoplasm, both ana- 

 tomical and physiological, and the chemico-physical and 

 morphological properties of the nucleus. In a short 

 section he discusses the question, Do elementary or- 

 ganisms exist without nuclei ? i.e. Can you have little 

 clumps of non-nucleated protoplasm pursuing an inde- 

 pendent life? As is well known, Haeckel described 

 organisms of this simple character, as cytodes, and 

 gave Monera as an example ; but Hertwig is disposed 

 to think that such non-nucleated organisms have not 

 been definitely demonstrated in the animal kingdom, 

 and he quotes Butschli's observations, which seem to 

 show that even in such micro-organisms as Bacteria a 

 differentiation of a nucleus from surrounding protoplasm 

 can be distinguished. 



Two important chapters are written on the movements 

 of protoplasm, of cilia, of flagella, of spermatozoa, on 

 contractile vesicles, and on the irritability of protoplasm 

 under the stimulus of heat, light, electricity and several 

 kinds of mechanical and chemical irritants. The fifth 

 chapter is devoted to the consideration of the nutritive 

 changes and formative activity in cells. Illustrations are 

 given of the power possessed by certain unicellular 

 organisms of taking into their substance and digesting 

 solid bodies of various kinds, and an account is appended 

 of the important observations of Metschnikoff on 

 phagocytosis. 



Chapters six and seven are occupied with a description 

 of the multiplication of cells, their mode of division, and 

 the method of fertilization. The process of karyokinesis 

 is described at some length and in its various phases, in 

 clear and precise language, and with an amount of 

 illustration which enables the reader to follow without 

 difficulty this complicated process. The influence 

 exercised by the nucleus, and the part which it plays in 

 the process of cell multiplication, has now been put by 

 the labours of many investigators on a basis of observation , 

 both as regards plants and animals, such as cannot be 

 controverted, and the accuracy of the generalization 

 made half a century ago, both by Martin Barry and John 

 Goodslr, that young cells originate through division of 

 the nucleus of a parent cell, has been amply established. 

 Dr. Hertwig also recites observations which seem to 

 show that the nucleus does more than act as a repro- 

 ductive centre within the cell, but also takes a part in 

 cell nutrition. This function of the nucleus was also 

 contended for by Goodsir, but during the period when 

 protoplasm was regarded as the essential element in 

 nutrition or secretion, the claim of the nucleus to take 

 any share in this phase of cell activity was summarily put 

 aside. Recent observations have, however, shown that 



