SPECIES IDENTITY OF NUCLEUS-PLASMA NORM 467 



crease of as much as 50 per cent, for the crayfish cells for as much 

 as one hundred per cent, namely to double the size of the starting 

 point cell. This so far invariable result is held, in the first place, 

 to give a wider basis for accepting the uniformity of relation 

 among various sized resting cells. Cells even more variant in 

 absolute size have an identical relation. Technically, it makes 

 the selection of cells for measurement much simpler. To re- 

 strict one's self to a hard and fast type of resting cell would 

 make the proposition very difficult, for one thing, for example, 

 in the matter alone of finding them in highly excited animals 

 such as were used. A somewhat broader range of selection 

 which was postulated on the basis of uniform relation is per- 

 missible. Slight indications of beginning activity, a little more 

 chromatin than usual for example in an otherwise conforming 

 type, make no difference. As a matter of fact, a few cells midway 

 l)etween rest and the maximum of the first stage of activity were 

 included in some experiments to see if the result was appreciably 

 affected. It was not (compare also Cell 16, table 2). Still, 

 since even within the strict resting type the cells do vary con- 

 siderably in absolute size, possessing only in the matter of size 

 the one common characteristic of nucleus-plasma ratio, the doubt 

 involved was put to the following actual test of calculation in 

 one series, in default of a mathematical investigation of the 

 probabilities and the reasons therefor, which is beyond the 

 writer's power. 



It must be kept in mind that the routine method of calcula- 

 tion employed was to take the average of the diameters of the 

 twenty-five cells in each series and from these average figures 

 the volumes and coefficients were calculated. In Experiment 

 Shock 37 which was chosen for a test of the accuracy of this, 

 the figure for the coefficient thus obtained is 12.37 (table 1). 

 Now, instead of using the diameters, the individual volumes of 

 the cells and the nuclei of this series were calculated from the 

 individual dimensions, and the volumes themselves averaged. 

 The resulting coefficient figure was also 12.37. Finally, the 

 average was taken of the series of coefficient figures obtained 

 from each individual calculation and the figure was 12.61. These 



