CHANGES IN WEIGHT OF: CENTRAL NERVOUS SYSTEM 671 
given in table 3. This table shows that the mean value of C 
rises from March 28th to a maximum in July and then begins to 
fall. In the case of one group, formed by the series 13, 14, 15 and 
16, there appears an unexpectedly small relative weight of the 
central nervous system, while at the same time there is no ground 
to exclude these series as abnormal. I assume therefore that the 
series forming this group came from localities where the frogs had 
a proportionately small nervous system and that these were not 
mixed as in the case of the other series, with frogs from more north- 
ern stations, in which the nervous system happened to be larger. 
For reasons given earlier, the autumn fall is very incompletely 
shown, but the observation of the January series gives, asone would 
expect, a value of C similar to that found in March. Asa control, 
I have calculated the probable error of the mean (+ .6745 a 
\ n 
of C in all the groups of table 3. 
As will be seen, in the groups that consist of four series, this is 
quite constantly about 0.3. This value is high but when it is 
considered that the ranges of the value of C in the several series 
TABLE 3 
Data on frogs from Chicago, 1901-02 
| ene a, VALUE OF C PERCENTAGE OF WATER 
SERIES an oi MEAN DATH ita |e yt ; a 
| Probable 
ifs We aie Mean error of Brain Cord 
| mean 
| 1901 | | 
1 eee st it March: | 28 | .o47 | #016) 84.1 | 79.5 
DATS Atte 12). (8 \ April 9 | 25.8 | +0.32| 84.6 80.3 
Fees, ote 16. “| 1a | May Ao DIO aOR IO pee gy 80.7 
OSi2h or.) 14 oid. Jone 1” |) e276 ls Orato s4aG 80.6 
a= Ge hale eto June 29* | 25.8: |) 20:27 |e 85.1 80.5 
E20 MealiG) ot lay t dhaly oF | 28:5 0 iy sOnsteh 6847 80.1 
PI el TAS | 4 4) August 94 |. “28.5. Ors" 8458 80.4 
25-28......; 12 | 14 | September 22 97.9 | +£0.32) 84.5 80.2 
1902 | | 
iene aes Bop 22 January 30 24.8 | +0.67 84.6 81.1 
*See Comments on p. 671. 
