September 1, 1911] 



SCIENCE 



281 



solution, where the small hanging drop of 

 saline frequently spread out and the tissue 

 was left closely adherent to the cover slip. In 

 two such cases, and in a similar one in which 

 serum was used, cell movements took place, 

 but the cells which exhibited movements were 

 all in contact with the lower surface of the 

 cover. One case showed nerve fibers. In 

 another interesting case the drop of culture 

 fluid was larger and touched the bottom of the 

 chamber. The piece of tissue sank to the 

 bottom and became adherent, sending out a 

 number of short hyaline protoplasmic proc- 

 esses along the surface of the glass. 



These and previous experiments show, then, 

 that the movements of embryonic cells take 

 place when the cells are in contact with a 

 fibrin net, the fibers of a spider web or the 

 surface of glass coverslips and slides, and that 

 they occur in a considerable variety of fluid 

 media. On the other hand when the embryonic 

 tissue is suspended free in a drop of fluid," no 

 cell movement takes place, though differen- 

 tiation of tissue may result. In this move- 

 ment and orientation of the cells we have 

 before us a form of stereotropism, of which, 

 however, the exact nature remains for the 

 present undetermined. Whatever it may 

 prove to be, it can scarcely be doubted that 

 it is an important factor in normal develop- 

 ment, influencing the movement and segrega- 

 tion of pigment, mesenchyme and nerve cells 

 at least, and probably also the growth move- 

 ments of nerve fibers. 



Eoss G. Harrison 



Sheffield Biological Laboratory, 

 Yale TJniveesity 



°M. E. and W. H. Lewis {op. cit.) state that 

 growth apparently takes place as well in fluid 

 media as in solid, though they admit that the out- 

 growing cells often creep on the cover glass or 

 the bottom of the dish. I feel confident that care- 

 ful examination of specimens with reference to 

 this point will show that the growing cells are 

 always in contact with the glass, except that the 

 surface film of the free hanging drop may some- 

 times act as a substitute for the solid surface, as 

 I have occasionally found to be the case in a 

 series of experiments with tissues of the chick 

 embryo, to be described later. 



ON" THE INCREASE IN OXIDATION IN THE EGG AT 

 THE BEGINNING OF DEVELOPMENT 



It was observed by 0. Warburg that the 

 oxidation in the sea-urchin's egg is increased 

 when it is fertilized or placed in a hyper- 

 tonic solution, which induces parthenogenesis. 

 Warburg observed an increase in oxidation in 

 the fertilized egg when placed in pure NaCl 

 solution (which also causes parthenogenesis 

 in the unfertilized egg), but in order to insure 

 the life of the eggs long enough for the ex- 

 periment he added a trace of NaCN to the 

 NaCl (and to the control). 



The addition of NaCN was objected to by 

 Loeb and Wasteneys, who found no increase 

 in oxidation if the cyanide was omitted. 

 Apparently the cyanide, or hydroxyl ions lib- 

 erated by hydrolysis, had something to do with 

 the result. We found that NaCl increased 

 oxidation in unfertilized eggs about one 

 fourth. 



We made similar experiments on unfertilized 

 eggs using an isotonic NaCl solution contain- 

 ing the same hydroxyl ion concentration as the 

 sea water (made by the addition of NaOH). 

 The result was an increase in oxidation in the 

 NaCl solution to double its rate in sea water. 

 In other words, the NaCl solution in the pres- 

 ence of OH-ions causes an increase in oxida- 

 tion in the unfertilized egg. This was found 

 true also of another parthenogenetic agent. 



Microscopic examination showed that the 

 eggs formed " fertilization membranes " in the 

 ISTaCl solution, and some of them that were 

 returned to sea water after the close of the 

 experiment segmented and produced cilia. In 

 short, the NaCl -|- OH ions start develop- 

 ment and the increased oxidation may be due 

 to the same cause as the increased oxidation 

 in the fertilized egg. 



One of the authors has shown an increase 

 in permeability of the egg to ions, at the 

 beginning of development. He suggests that 

 the NaCl solution causes an increased per- 

 meability of the egg to OH-ions, and that the 

 latter penetrate the egg and accelerate oxida- 

 tion. The morphological changes in the egg 



