GROUPS OF FLUCTUATING VARIATION 561 



in the egg of the sea urchin Strongylocentrotus purpuratus 

 can be so sharply measured and is so nearly constant that it 

 can be used for the establishment of a temperature coefficient 

 and this was later confirmed by Loeb and Wasteneys^ for the 

 egg of Arbacia. Since the influence of temperature is again of 

 the high order characteristic of chemical reactions, we may make 

 the assumption that each egg carries a definite mass of one or 

 more enzymes or catalysers which determine the rate of cell 

 division. If we fertilize a mass of eggs of the same female of 

 Arbacia and keep them at the same temperature, we find that 

 they do not all begin to segment at the same time, and that 

 there is an interval between the cell division of the first and 

 last egg of the group. If we assume that the velocity of 

 the cell division is determined by the mass of enzjrmes and the 

 temperature, the fact that at t° some eggs divide after 100, 

 others after 101, 102, until, e.g., 113 minutes, we must con- 

 clude that this difference in time is the expression of a corre- 

 sponding difference in the mass of enzymes in different eggs, 

 those dividing in 100 minutes having a greater mass of enzymes 

 than those dividing in 102, 103, etc., and 113 minutes; and that 

 the mass of enzymes varies in inverse proportion to the time 

 required for cell division at a given temperature. On this basis 

 we should have to assume that the latitude of variation in the 

 rate of cell division of a group of eggs is the expression of a 

 corresponding variation in the mass of enzyme in the individual 

 eggs. This idea can be put to a test with the aid of the tem- 

 perature coefficient. If we call m the minimum mass of the 

 enzyme responsible for the first cell division in the slowest eggs, 

 then we shall find a certain greater percentage of eggs with the 

 enzyme mass m + a, a still larger percentage with the mass 

 m + 0^2, and a small number with the mass m + «« where m +. an 

 is the greatest mass of enzyme occurring in an egg. If the eggs 

 with the mass m + an divide at the temperature t° after 100 

 minutes, they will divide in about Qio X 100 minutes at the 

 temperature (t - 10)°, where Qio is the temperature coefficient 

 for 10°C. at this point; the eggs with the smallest mass of enzyme 



^ J. Loeb and H. Wasteneys. Biochem. Ztschr., 36, 345, 1911. 



