64 



NATURE 



[May 19, I : 



particle which is present, sometimes in the nucleus, oftener in 

 the external cytoplasm, and which is by many assumed to play 

 the part of a direcli%-e agent in the matter of nuclear division. 

 This body, known as the Centrosome, was first brought into 

 prominence by the researches of Van Beneden on the develop- 

 ing eggs of Ascaris, and it has since been recognised in an 

 enormous number of animals, and also in the cells of some 

 plants. 



The centrosome is frequently a body of extraordinary minute- 

 ness, and it is most easily recognised during certain stages of 

 nuclear division, on account of the central position which it 

 occupies with respect to the radiations which accompany the 

 process. 



It has, however, been identified in many cells which are in a 

 state of repose, as a minute particle which may or may not be 

 -surrounded by differentiated zones of specialised protoplasm, 

 though it is certain that in many cases this appearance is due 

 merely to a diffraction-phenomenon. Furthermore, it is not un- 

 frequently observed that its division precedes any change in the 

 nucleus, and that when the division of this latter body is 

 approaching, the two daughter centrosomes diverge from each 

 other, each situated in a definite protoplasmic mass and form- 

 ing one of the two poles of the spindle structure which arises 

 during the process of karyokinesis.^ Sometimes, indeed, this 

 spindle structure is seen to be spun out, as it were, between the 

 two centrosomes at the moment of their separation, and to grow 

 as they move further apart. Even more important, perhaps, 

 than these observations was the statement made by Fol, that 

 during the process of fertilisation both the male and female cells 

 contributed a distinct centrosome, each of which then divided, 

 and the half of the one then fused with the corresponding half 

 of the other, a proceeding to which he gave the name of the 

 Quadrille of the Centrosomes. This statement, which was 

 supported by precisely similar statements on the part of Guignard 

 for plants, as well as by other zoologists, has, however, proved 

 to be due to misinterpreted or mistaken observation. It is quite 

 certain that at present there is no really authenticated example 

 of such a proceeding occurring either in plants or in animals, 

 although a glance at many modern text- books testifies to the 

 hold which these erroneous accounts have taken on receptive 

 minds. 



In the enthusiasm to which the first discovery of the centro- 

 some, and its subsequent identification in so many kinds of cells, 

 gave birth, it has not always perhaps been sufficiently remem- 

 bered ihzX post hoc by no means necessarily implies /ro//^r hoc : 

 and that neither its reappearance at the period of karyokinetic 

 activity, nor yet its observed persistence through the resting 

 stage in some cells, are of themselves sufficient to establish its 

 claims to be regarded as Xh^ primary directive agent in bringing 

 about a nuclear division. Supposing, however, that it could be 

 shown to be really possessed of all the occult powers which have 

 been claimed for it by its numerous devotees, the main result 

 would be to remove to an immeasurably greater distance all 

 chance of penetrating more deeply into the mysteries of cell life. 

 For its very minuteness renders it almost immune from the 

 critical gaze of the curious. 



Possibly some light may be thrown on the method of action 

 (if indeed it really possesses any at all) of this enigmatical body, 

 by a consideration of some of the cases in which it cannot be 

 said to exist at all. For some years past it has been known 

 (and the number of examples has been recently multiplied) 

 that in certain plants the nuclear division is not inaugurated by 

 the appearance of two diverging centrosomes, which could 

 occupy a definite position with regard to the radiations at this 

 time visible in the protoplasm. On the contrary, radiations 

 start out from many centres in the cell, and run in various 

 directions, though with a general tendency towards the nucleus. 

 Later on these numerous centres become, so to speak, polarised, 

 and commonly come together at two principal points occupying 

 opposite ends of the cell. Thus a final condition of affairs is 

 reached, resembling the more regular arrangement obtained by 

 the centrosome mechanism (Figs, i and 2). What starts these 

 radiations in the first instance ? It is difficult to imagine them to 

 be otherwise than due to a chemical change in the protoplasm, 

 or of some of its included substances, and this view is strength- 

 ened by the observations made by Hertwig and others on the 

 stimulating and modifying action of drugs, such as quinine or 

 strychnine. Morgan, by merely altering the salinity of the sea- 



1 A word used to signify nuclear division, introduced by Schleicher ; it 

 is equivalent to the term Mitosis, employed by Flemming. 



NO. 1490, VOL. 58] 



water, was able to produce centrosomes and radiations at will, 

 and the irregularity in number and size which they displayed was- 

 just such as might have been expected, on the hypothesis here 

 advanced. 



These observations — and many similar ones could be cited — 

 go to show that the impulse to division, which some have triedl 

 to identify exclusively with the centrosome, is more probably 

 dependent on the condition of the protoplasm as a whole. It 

 is quite probable that, as in so many other cases, the stimulus may 

 be at bottom a chemical one, connected with the elaboration 

 of some substance producing the disturbances which result ini 

 the formation of the machinery for cell division. It is even 

 possible that the substance may, in the more .specialised cells, 

 or in those of rapidly dividing tissues, be aggregated into a 

 mass which assumes the manifold appearance that one finds \n 

 the centrosomes, centrospheres, and so on. From what we know 

 of protoplasm it would hardly be surprising if this were so. 

 Carbohydrate can be stored as starch, to be again lost to sight 

 as sugar, &c. ; why not the substance which may be supposed 

 to be capable of reacting with the rest of the protoplasm in the 



production of the karyokinetic phenomena ? But this is a very 

 diff"erent thing from considering the centrosome as. a sort of 

 autocrat presiding over the destinies of the cell, as its more en- 

 thusiastic supporters have claimed. It would not even be 

 necessarily & permanent structure inaugurating the cell changes, 

 but would represent a substance, which might merely be formed 

 ad hoc, and which, after the period of activity, might either 

 lose its identity — sinking to the general level of the substances 

 contained in the protoplasm — or if present, in sufficient quantity, 

 over and above what proved to be needed for a given occasion, 

 it might remain as a formed substance to be used up later. 



There is a large body of evidence to show that, when present, 

 it is intimately associated with the processes of nuclear division, 

 though whether in an active or passive connection it is diffi- 

 cult, perhaps impossible, to say. Certainly, taking the most 

 favourable view as to its autocratic powers, it can efifect nothing 

 unless the protoplasm be ready to receive it. The centrosome of a 

 spermatozoid introduced into a ripe egg may become the centre 

 of a system of radiations, but none are produced if the ovum 

 happens to be immature. And on the whole, especially in view 



