466 J. RUNNSTROM 



basis of, for example, centrifuge experiments. The consistency may vary 

 in different regions in the cytoplasm as Allen and Allen and Roslansky 

 have confirmed in an elegant way by studies on amoeba [i, 2]. What we 

 study by centrifugation experiments or by other methods may seem in the 

 first place to be the consistency of the ground cytoplasm or matrix in which 

 the other components are embedded. The centrifugation and other 

 methods may thus be able to give us certain information about the changes 

 which occur in the matrix. These changes may indeed be impressive. A 

 stratification of the inclusions occurs very readily when an unfertilized egg 

 of the sea urchin Arbacia is submitted to an acceleration of 4000-5000 x g 

 for some minutes, whereas 15 min. after fertilization practically no 

 stratification occurs under the same conditions. These variations in 

 consistency have been particularly studied by Heilbrunn and co-workers 

 [6, 7, 8]. The ground cytoplasm is evidently a very complicated system. 

 It contains a number of elements among them certainly fibrous proteins 

 that may be mainly responsible for the changes in consistency. These changes 

 are often characterized as gelations or solations, which expressions indicate 

 variations in the intermolecular binding forces. We look forward to the time 

 when electron microscopy will be able to demonstrate such changes in the 

 cytoplasmic matrix. As gelations and solations may be localized in definite 

 regions of the cell they may play a role in the cell machinery, particularly 

 in the division of the cell and in difi^erentiation. 



Contraction may be regarded as gelation in an accidentally or per- 

 manently oriented fibrillar system. Its role in amoeboid movements will 

 be analvzed in Dr. Allen's paper, whereas Dr. Gustafson will demonstrate 

 the great role that apparently random cell movements play in bringing 

 about strictly regulated morphogenetic processes. 



In Fig. I I have roughly outlined a curve from a paper in press [23]. 

 The unfertilized eggs of the sea urchin Paracentrotus lividus were exposed 

 for 15 min. to varying concentrations of crystalline trypsin. After the 

 treatment the eggs were thoroughly washed with pure sea water. There- 

 after the eggs were fertilized. When trypsin concentrations of io~^-io^* % 

 were used the pretreatment caused blockage of segmentation in maximally 

 80-90% of the eggs. The blockage was evidently due to a gelation of the 

 cytoplasm. This was also confirmed by centrifugation. Even before 

 fertilization a decreased stratification was observed in those eggs that had 

 been pretreated by trypsin concentrations in the range of maximum effect 

 on the cleavage. The gelation caused by lower concentrations of trypsin is 

 reversed by higher concentrations of the enzyme. ATP in concentrations 

 of 5 X 10^^ M enhances the gelation effect if it is added after a pretreatment 

 of the eggs with a trypsin concentration that is not sufficient to bring about 

 the maximum gelation of the cytoplasm, cf. first arrow from the left in 

 Fig. I. Added ATP may in such cases bring the eggs to the maximum 



