I lo CELL-DIVISION 



tring in two adjacent points. This result is obtained by warming and 

 then cooling a film of thick gelatine-solution, filled with air-bubbles, 

 and then coagulating the mass in chromic acid. Such a film shows a 

 fine alveolar structure, which assumes a radial arrangement about the 

 air-bubbles, owing to the traction exerted on the surrounding structure 

 by shrinkage of the bubbles on cooling. The amphiastral simjilacra 

 are produced about two adjacent bubbles, — a " spindle " being formed 

 between them, and the " astral rays " sometimes showing a crossing 

 like that seen in the actual amphiaster (Biitschli is himself unable to 

 explain fully how the crossing arises). The protoplasmic asters are 

 maintained by Biitschli to be, in like manner, no more than a radial 

 configuration of the alveolar cell-substance caused by centripetal 

 diffusion-currents toward the astral centres.^ The most interesting 

 part of this view is the assumption that these currents are caused by 

 specific chemical cJianges taking place in the centrosome which causes 

 an absorption of liquid from the surrounding region. ** The astral 

 bodies are structures which, under certain circumstances, function in 

 a measure as centres from which emanate chemical actions upon pro- 

 toplasm and nucleus ; and the astral phenomena which appear about 

 the centrosomes are only a result incidental to this action of the central 

 bodies upon the plasma." ^ Through centripetal currents thus caused 

 arise the asters, and they may even account, in a measure, for the move- 

 ments of the chromosomes.^ This latter part of BiitschU's conception 

 is, I believe, quite inadequate ; but the hypothesis of definite chemical 

 activity in the centrosome is a highly important one, which is sustained 

 by the staining-reactions of the centrosome and by its definite morpho- 

 logical changes during the cycle of cell-division. 



More or less similar chemical hypotheses have been suggested by 

 several other writers.^ Of these perhaps the most interesting is 

 Strasburger's suggestion,^ that the movements of the chromosomes 

 may be of a chemotactic character, which I suspect may prove to have 

 been one of the most fruitful contributions to the subject. Beside this 

 may be placed Carnoy's still earlier hypothesis ('85), that the asters 

 are formed under the influence of specific ferments emanating from 

 the poles of the nucleus. Mathews ('99, 2) has recently pointed out 

 that there is a considerable analogy between the formation of the 

 astral rays and that of fibrin-fibrils under the infiuence of fibrin-fer- 

 ment, adding the suggestion that the centrosome may actually contain 



1 Carnoy ('S5) and Plainer ('86) had previously held a similar view, suggesting that not 

 only the spindle-formation, but also the movements of the chromosomes, might be explained 

 as the result of protoplasmic currents. 



2 '92. I, p. 538. 



8 '92, 2, p. 160; '92,3, p. 10. 



* Cf. the first edition of this work, p. 77, also Ziegler ('95). ®'93» 2. 



