432 



NA TURE 



[August 22, 1907 



Ihe positions originally occupied by the respective colloids 

 during life, there is no real force in the objection. No 

 one would call in question the accuracy of a photographic 

 negative on the ground that after development it no longer 

 consisted of the actual substances which had been formed 

 in the film by the exposure to the action of light. All 

 that is required is that the deposited silver shall accurately 

 express the limits of, and be proportionate in amount to, 

 the alteration in the composition of the salt which was 

 produced when the plate was exposed in the camera. 



.Much of the general detail of a nuclear division can be 

 followed even in the living cell, and we therefore possess 

 direci as well as indirect means of testing the degree of 

 accuracy with which the fi.xcd preparation represents the 

 rriginal pattern of distribution of the colloids within the 

 cell. No one who has studied the behaviour of artificially 

 prepared mixtures, the colloidal proteins and nucleins after 

 " fixing " and staining them, can entertain reasonable 

 doubts as to the substantial identity of the structures 

 visible in a well-fixed cytological preparation with those 

 present during life. For the substances, even in these 

 artificial mixtures, keep remarkably distinct, as indeed 

 Fischer showed some years ago. 



Few things are more striking than the remarkable series 

 of evolutions passed through by the linin, and by the 

 chromosomes which finally emerge from it during the 

 progress of a mitosis. We have clear evidence that the 

 nucleus at this period is the seat of rapid chemical change. 

 The process of distribution of the nuclein within the linin 

 is sufficient proof in itself of this. But we have also, I 

 believe, evidence of physical disturbances of an electrical 

 nature which accompany, and indeed in a measure deter- 

 mine, the course of mitosis. This is indicated, not only 

 bv the movements that proceed within the nucleus, and 

 concern the linin and chromosomes, but also by the re- 

 markable alterations in surface-tension exhibited by the 

 nuclear membrane. 



It is well known that at a certain stage of the hetero- 

 tvpe division, for example, the chroiriosomes move to the 

 periphery of the nucleus, and each one is removed as far 

 as possible from every other chromosome. At this stage, 

 to which Haecker has given the name of " diakinesis, " 

 the nucleus reaches its maximal size. Diakinesis is not 

 the only stage in which there is an indication of repulsion 

 between the elements of the chromatic linin. Measure- 

 ments prove that all such periods of repulsion are also 

 marked by an increase of nuclear size which is transitory, 

 and either disappears or alters in a synchronous fashion 

 with them. These phases of enlargement have been 

 generally regarded as directly connected with the intake 

 of liquid by the nucleus, due to a hypothetical change in 

 o;;motic conditions. But, so far as 1 am aware, no satis- 

 factory explanation has yet been given as to why, or how, 

 the supposed increase of osmotically active molecules 

 within the assumed semi-permeable nuclear membrane 

 could be effected. On the other hand, an enlargement of 

 the surface-membrane of the nucleus w^ould necessarily 

 follow on the migration towards it of chromosomes or 

 other bodies carrying similar electrical charges. For the 

 induced charge in the particles of the membrane would of 

 course weaken its coherence, for the same reason that the 

 free chromosomes repel and move away from one another. 



There is evidence to show that the proteins are able to 

 carry such charges, and this is a matter of the highest 

 importance as affording a clue to many other processes in 

 which changes of surface-tension play a part, besides those 

 connected with nuclear division. 



Not the least of the many remarkable properties exhibited 

 by the proteins lies in their capacity of taking on either 

 a positive or a negative charge of electricity. A clear 

 proof of this was afforded by the beautiful experiments of 

 Billitzer, who showed that, when so charged, the colloid 

 moves as a whole towards one pole or the other on send- 

 ing a current through the liquid in which it was suspended. 

 At first sight it may not be easy to understand how it is 

 possible for a colloid to receive and retain a charge under 

 the conditions which obtain either in the solution or in 

 the cell. It must, how-ever, be remembered that the liquid 

 contains electrolytes in solution also, and any disturbance 

 in the equilibrium of the products of ionic dissociation 

 will be accompanied by corresponding differences of 



NO. 1973, '•'OL. 76] 



potential. The most reasonable explanation of the pheno- 

 menon in question seems to be that the colloids are un- 

 equally permeable lo the iojis, whereby there comes to be 

 a preponderance of one or the other group associated with 

 the proteins. Perhaps this should be connected with the 

 remarkable though still imperfectly understood property of 

 adsorption which is characteristic of many colloids. 



Much, however, still remains to be done before a com- 

 plete survey of the electrical changes that are associated 

 with mitosis can be made. We especially desire more com- 

 plete information on the nature of the chemical processes 

 which are involved. For it is obvious that the physical 

 changes must ultimately be connected with the transform- 

 ation of materials which goes on so energetically at these 

 recurrent periods of nuclear activity. We do not yet know 

 how or why the chromosomes that have been dispersed at 

 diakinesis should again congregate on the spindle prior to 

 their final separatioji. Possibly this is to be connected 

 with the signs of disturbance in the extra-nuclear cyto- 

 plasm, which in its turn finds expression in the differenti- 

 ation of the achromatic spindle. The character of this 

 body has long aroused the suspicion that its existence is 

 to be attributed to electrical causes. The more recent 

 work serves to indicate that this suspicion w'as well 

 founded. 



The more complete study of the chemistry and physics 

 of karyokinesis is certain to prove valuable for another 

 reason. The successive changes which the nuclei of both 

 animals and plants exhibit when they are undergoing 

 division are so remarkably similar that it seems exceed- 

 ingly probable thai the processes actually involved may 

 turn out to be relatively simple, at any rate in their broader 

 features. I mean that they probably belong to what we 

 might term the lower grade of metabolic problems. For 

 the great uniformity of the process as a whole, complex 

 though it undoubledly is, hardly sugges.ts direct relations 

 as existing between it and those more specialised forms 

 of metabolism on which the properties of specific form, 

 and such like characters, depend. This view of the matter 

 is not in any way weakened by the fact that the materials 

 providing for the multiplication of nuclei have themselves 

 passed through the very highest stages of anabolic con- 

 struction. There are, indeed, some grounds for believing 

 that the composition of the higher, proteins is distinctly 

 specific for different groups of organisms ; but apart from 

 this it is difficult to resist the conviction that, in so far 

 as its .essential constituents are concerned, the nucleus is 

 the seat of a complex organisation which is superadded to 

 its chemical composition. But this conception of the 

 nucleus does not affect the position of the lower-grade 

 chemical changes, with their physical accompaniments 

 which are periodically rendered apparent during the rhyth- 

 mical .series of changes that culminate in the division of 

 the nucleus. It is true that there are some who refuse 

 to admit the necessity of what I might jjerhaps call archi- 

 tectural complexity in protoplasm. They prefer to regard 

 all the phenomena of organisation and heredity as the 

 outcome of dynamical, rather than of structural, con- 

 ditions. It seems to me that it is impossible to. reconcile 

 such a view with the known facts respecting the inherit- 

 ance of characters, and that we are driven to postulate 

 the existence of material units which are to either re- 

 sponsible for the sum of the characters represented in any 

 individual. There are grounds for believing that their 

 entities, whatever be their nature, are doubled, and then 

 equally distributed to the two daughter cells at every 

 ordinary nuclear division ; and thus the properties of 

 organisation are pn-served and transmitted over and above 

 the flux of chemical change. 



Most people who have concerned themselves with cyto- 

 logical studies agree that the salient features of karyo- 

 kinesis strongly emphasise the probability of a conservation 

 of definite material ; and that an extremely accurate dis- 

 tribution of it occurs where two daughter cells arise from 

 a parent cell by division. And this inference is greatly 

 strengthened by what occurs, more or less immediately, 

 in connection with the formation of the sexual cells. The 

 origin of these in all the higher animals and plants, as 

 is well known, can invariably be traced to a nuclear 

 division of remarkable complexity. In this, the so-called 

 heterotype division, the special feature consists in the 



