May 



I9I3J 



NATURE 



that are thereby produced. He regards diffusion 

 as brought about by currents which radiate to 

 and from the centres of greatest concentration ; 

 when a drop of solution of higher concentration 

 is placed in a solution of lower concentration, the 

 drop becomes the centre of symmetrically radiating 

 currents, the one set, consisting of the solution 

 of higher concentration, radiating outwards 

 (centrifugal), the other set (centripetal) radiating 

 inwards and consisting of the solution of lower 

 concentration. "The force producing the currents 

 is the osmotic pressure. Their centres of emis- 

 sion, true dynamic centres or poles, are of two 

 kinds : centres of osmotic pressure greater than 

 that of the medium or positive poles of diffusion, 

 and centres of lower osmotic pressure or negative 

 poles of diffusion. Around these poles of diffusion 

 the dynamic and kinetic phenomena are the same 

 as those which exist in the aether around electrii 

 or magnetic poles ; the same mechanical laws con- 

 trol them, and a molecule is displaced in the liquid 

 exactly like an ion in an electric field." Photo- 

 graphs are given by Prof. Leduc which show 

 that, for example, a drop of tinted water diffuses 

 into a saline solution along lines which exactly 

 correspond with the discharge from an electric 

 point or with the lines of force from the pole of 

 a magnet. " It is the graphical representation 

 of a centre of force such as was demonstrated by 

 Faraday." Concentric circles of concentration 

 are produced by diffusion which correspond with 

 Faraday's equipotential surfaces. 2 



Bv utilising differences of concentration and 

 the accompanying osmotic and chemical pheno- 

 mena under different conditions and with different 

 substances and media, Prof. Leduc states that he 

 has been able to reproduce many phenomena which 

 have hitherto been regarded as characteristic ex- 

 clusively of living matter. Of a few of these a 

 brief description is appended. 



Cell Synthesis. — Of the many different types of 

 cell which Prof. Leduc states that he has " syn- 

 thesised," the photograph, Fig. 1, shows three 

 varieties : A is an artificial cell produced by a 

 drop of solution of triammonium phosphate in a 

 solution of sodium carbonate and trisodium phos- 

 phate; the "nucleus" is large and the analogues 

 of the protoplasmic processes and the enveloping 

 membrane thick. The middle fio-ure B is an arti- 

 ficial aster produced by a drop of water tinged 

 with Indian ink in a solution of potassium nitrate. 

 C shows an artificial cell with interior granula- 

 tions. When such cells are prepared with a pre- 

 cipitated membrane composed, for example, of 

 calcium carbonate or phosphate, they grow in 

 size owing to the fact that the centripetal diffusion 

 (of water) is greater than the centrifugal, the 

 surrounding membrane becomine correspondingly' 

 extended. 



2 Reference may here be made to a paper by Dr. Horace T. Brown and 

 F. Escombe on static diffusion of eases and liquids, &c. (Phil. Trans., 

 1900, 193 B, 223), which is not referred to bv Prof. Leduc, but substantially 

 corroborates his views on the^e points. In this paper it is shown that the 

 lines of flow of gas or solute diffusine through a perforated diaphragm are 

 the analogues of the lines or tubes of force, and the shells of equal density or 

 ie analogues of electrical surfaces of iquipotenlial. 



Karyokincsis. — The reproduction artificially, by 

 very simple means, of all the phenomena character- 

 istic of karyokinesis is one of the most striking 

 achievements to which Prof. Leduc lays claim. 

 The photograph (Fig. 2) shows four successive 

 periods of cell-division reproduced by diffusion. 

 " If in a saline solution there is introduced between 

 two tinted drops, of less or greater concentration 

 than the solution and representing the centrosomes, 

 a drop of solution very slightly more or less cm 

 centrated than the solution and representing a 

 nucleus, all the transformations, all the movements, 





Wj, 



tration ob 



NO 



and all the figures characteristic of nuclear division 

 are seen to unfold themselves in their proper 

 sequence and regular order." In the figure A 

 shows the spirem stage, B the orientation of the 

 chromatic substance in the equatorial plane, C 

 the chromosomes on their way to the centrosomes, 

 and D the two final cells produced as a result of 

 the action. 



Multiplication. — If an artificial cell is kept for 

 a sufficient time in the liquid from which it has 

 been formed, after a time a furrow appears in 

 the interior of the cell and later other furrows 



appear which split up the cell into secondary cells, 

 the number of which rapidly increases until the 

 artificial cell becomes nothing but a group of 

 secondary cells — that is, an "artificial morula." 

 Fig. 3 shows a comparison of the germinative disc 

 of a hen's egg (A) with the segmentation of an 

 osmotic cell produced artificially. 



Nutrition and Development. — In a chapter on 

 the physiology of nutrition, illustrated by a number 

 of striking photographs which we cannot repro- 

 duce here, Prof. Leduc contends that the "facul- 



2272, VOL. 91] 



