March 6, 1915] 



NATURE 



5 



said of the discoveries of which we are speaking ; 

 moreover, such an opinion, too frequently re- 

 peated, should be rejected. If one looks closely, it 

 is possible to recognise that, in the majority of 

 cases, not blind fortune is the aid of the happy dis- 

 coverer, but the special attitude of mind and the 

 scientific preparation he possesses. In the concrete 

 case it is evident that Thomson, from the com- 

 mencement of his researches, was unconsciously 

 preparing- himself for the grand discovery of the 

 true nature of the kathode rays. It is sufficient in 

 proof of this to cite his noteworthy memoir of 

 1 88 1, relative to the electrical and magnetic effects 

 produced by the motion of electrified bodies, for 

 which Crookes's theory of radiant matter had 

 furnished the inspiration. 



The work published by Sir J. J. Thomson during 

 recent years constitutes the complement and 

 crown of his principal achievement. Thus, in a 

 short time he was able to collect into a body of 

 doctrine everything which relates to the propaga- 

 tion of electricity in gases, and of which his well- 

 known treatise on the subject is the embodiment 

 of the faith — a work that is consulted by all who 

 conduct experimental researches in this field, 

 which is very far from having yielded all its fruits. 

 In this volume are treated with much detail the 

 production of ions in gases, their disappearance, 

 their velocities under certain contingencies, &c. 

 Frequently the original experiments of the author 

 and his students have rendered possible the com- 

 pletion of the explanation of a particular pheno- 

 menon, or put in evidence some new detail or 

 the laws which it obeys. Moreover, making 

 use of the facts thus accumulated and the relation- 

 ship existing between them, Thomson had at his 

 disposal the elements necessary to found a theory 

 of electrical discharge more comprehensive than 

 any previously proposed, which, although not yet 

 complete and definitive, has enabled him to point 

 out the relations between facts apparently dis- 

 parate which previously could only be described 

 separately and disconnectedly. 



Quite recently the activity of the Cambridge 

 physicist seems to have been concentrated on the 

 study of the properties of the positive rays, and 

 especially of the so-called canal rays. This is 

 a field of studies in which several most daring 

 workers (Wien, Stark, &-c.) have amassed a rich 

 harvest of most important results; none the less, 

 I. J. Thomson, by the adoption of ingenious 

 experimental arrangements, in part new, and 

 especially by virtue of happily inspired and most 

 original interpretations, has drawn, and continues 

 to draw, from his researches consequences the 

 NO. 2 2 62. VOL. 91] 



import of which far surpasses the limits in which 

 they might have been expected to be confined. 



Of these researches physicists await with some 

 impatience the publication of a treatise which 

 shall present them not merely in order of date, 

 but with that arrangement, clearness and con- 

 cision which are precious characteristics of Thom- 

 son's writings. 



However insufficient and incomplete, the fore- 

 going considerations will help to make clear the 

 signal value of Thomson's work. Such, at least, 

 has been my intention. Although compelled to 

 abandon an analysis of the extensive scientific 

 productions of the great physicist, I trust that 

 all will be, like myself, convinced that his work 

 belongs to the category of those investigations 

 which leave an indelible impress on the progress 

 of science. Augusto Righi. 



AN ENGLISH TEXT-BOOK OF 

 PROTOZOOLOGY. 



An Introduction to the Study of the Protozoa: 

 zvith Special Reference to the Parasitic Forms. 

 By Prof. E. A. Minchin, F.R.S. Pp. xi + 520. 

 (London: Edward Arnold, 1912.) Price 2\s. 

 net. 



THIS work on the Protozoa by Prof. Minchin 

 may be considered as an attempt to confine 

 a knowledge of the philosophical and the prac- 

 tical side of the modern science of protozoology 

 within the limits of one volume. 



After discussing the one-celled organisms 

 grouped for convenience under the term Protista, 

 their modes of life are considered. Various types 

 of nutrition — purely animal, plant-like, feeders on 

 decaying matter, and finally parasitic methods — 

 are described and illustrated. The "mutual aid" 

 associations of the animal world known as sym- 

 biotic unions are charmingly portrayed, and in 

 contrast the interrelations of hosts and parasites 

 are set forth. A most interesting study in animal 

 mechanics is presented, together with a broad 

 account of the organisation of the Protozoa. To 

 the cytologist there is much of interest in the 

 chapter dealing with the nucleus and nuclear 

 structure. The author draws a distinction "be- 

 tween organisms of the ' cellular ' grade, with dis- 

 tinct nucleus and cytoplasm, and those of the 

 ' bacterial ' grade, in which the chromatin does not 

 form a distinct nucleus." He considers that a 

 "bacterial type of organism" is "not to be re- 

 garded as a cell, but as representing a condition 

 antecedent to the evolution of the true cellular type 

 of structure." Such a distinction seems somewhat 

 arbitrary and unnatural, and tends to overlook the 

 importance of intermediate forms. 



