DEVELOPMENT OF THE FROG'S EGG. 277 



The 17 per cent, sugar exerts a pressure of about 1 1.86 atmos- 

 pheres above that of the normal medium in which these eggs 

 live. The eggs were effected very readily under such conditions. 

 After only six hours in the solution a few showed no cellular 

 structure at all, while the others were far behind the control in 

 their rate of development. All died in late segmentation stages. 



The 20 per cent, cane sugar stopped the development of most 

 eggs within six hours, the blastomeres seemed to have fused 

 together. A very few eggs divided to about the sixth or sev- 

 enth cleavage and then underwent cytolysis. 



Lactose or milk sugar was tried but this substance dissolved 

 so slowly that it was difficult to interpret the results, and since 

 the maximum pressure of the solution was reached only after the 

 eggs had developed much beyond the 4-cell stage, the effects 

 are not readily compared with those resulting from the use of the 

 other sugars. 



Simple sugars, glucose and lsevulose, which are the inversion 

 products of the cane sugar molecule were tried in order to deter- 

 mine if possible whether solutions of these which were isotonic 

 with a given cane sugar solution would give similar results. 

 Approximate comparisons of these solutions may be made as 

 follows : A 5 per cent, solution of glucose or lsevulose exerts 

 a pressure nearly the same as a 10 per cent, solution of cane 

 sugar. It is not exactly the same since a molecule of cane sugar, 

 C 12 H 22 O u , is a little less than twice a molecule of glucose, 

 C.H.,0,, and in addition to this it must also be borne in mind that 

 equi-molecular solutions of glucose and cane sugar do not exert 

 exactly the same osmotic pressures, although for general pur- 

 poses the two are considered about equal. 



Eggs when in the four-cell stage were placed in the following 

 strengths of glucose, 2, 3, 3.5, 4, 5, 5.5, 5.8, 6, 6.5, 10 and 15 

 per cent. The 2 per cent, solution had a very weak action caus- 

 ing the development to proceed slower than usual. After forty 

 nine hours in the solution many of the eggs were slightly abnor- 

 mal. 



The 3, 3.5 and 4 per cent, solutions retard development con- 

 siderably within twenty hours, and those in the 4 per cent, solu- 

 tion show abnormal gastrulation with prominent yolk-hernias. 



