250 PROTOPLASM 



area may also be the effect of chemical alterations which are 

 produced by the central body. 1 



Although I consider this explanation only quite hypo- 

 thetical at present, nevertheless I thought it best not to omit 

 it, since I am convinced that we shall get no farther in these 

 matters by means of speculations upon attractions and con- 

 tractions, or with the help of micellar and molecular 

 theories, but that we must rather risk the attempt to ad- 

 vance upon the basis of the known phenomena of molecular 

 physics. In any case I think that by means of this work 

 I shall establish the conviction that in living matter there 

 are no mysterious forces at work, but only those which 

 also prevail in the organic world. 



My interpretation of the radiating appearances which are 

 visible during division is, however, still further supported by 

 the fact that similar appearances are to be seen quite un- 

 connected with division. I have already referred before 



1 See with regard to the questions here discussed a memoir by the author 

 entitled "Ueber die ktinstliche Nacliahmung der karyokinetischen Figur " 

 (On the Artificial Imitation of the Karyokinetic Figure) in the Verha/ndl. d. 

 nat. mcd. Vcrcins Heidelberg, N. F., T. V., Heft 1, where new observations 

 have led him to somewhat changed views. It is shown that in a foam of 

 gelatine and oil which has been warmed, a very distinct radial striation ap- 

 pears on cooling round little air-bubbles enclosed in it. The same occurs in 

 the case of air-bubbles enclosed in the foam-like structures shown by albumen 

 when coagulated by heat, and in coagulated gelatine (vide supra, p. 216). Each 

 such bubble may lie in a clear space, which passes into the sun-like system 

 of rays. This appearance is due to the contraction of the air-bubble on cool- 

 ing, which causes a tension or pull to be exerted on the surrounding mass. 

 The tension is directed from all sides towards the centre of the bubble, and 

 modifies the foam-like structure into a system of rays. When two such sys- 

 tems cross each other a spindle-like figure results. 



Hence the explanation of the radiate appearances round the centrosome 

 must be somewhat as follows. The centrosome does not diminish in volume 

 like the air-bubbles described above, but is known to increase in size during 

 the formation of the aster. This increase can only be due to its absorbing 

 fluid from the surrounding protoplasm. If it be supposed that the centrosome 

 becomes chemically combined with the fluid it absorbs, it will increase in size 

 to a less extent than the surrounding protoplasm diminishes by loss of the fluid 

 given up to the centrosome. Then the centrosome will form the middle point 

 of a portion of the protoplasm which is contracting and diminishing in size 

 as a whole, and this protoplasmic area will exert radially directed tensions 

 upon the remaining protoplasm and produce radiate appearances, just as in 

 the case of the contracting air-bubble. 



