BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 83 
confirmation of the statements just made concerning the similar- 
ity of the albinos on the two sides of the Atlantic. 
In this case of body length, as in that of the other data on the 
weight of the brain and spinal cord and on cranial capacity, to be 
presented later, the records are for the two sexes combined, since 
the differences according to sex are so small as to be negligible for 
the present investigation (Donaldson and Hatai, ’11). 
WEIGHT OF THE CENTRAL NERVOUS SYSTEM 
The establishment among the several series of the similarity in 
body form clears the way for the study of the weight of the central 
nervous system in these same series. The method of direct 
weighing is the simplest and, as it has turned out, the most satis- 
factory method of attacking the problem before us. Had I to 
repeat this investigation I should make only direct determinations 
on the weight of the brain and spinal cord and omit those on 
cranial capacity, but when the investigation was begun, it was 
thought that the longer series of cranial capacity determinations 
would be more valuable than a shorter series of direct weighings, 
which require withal more time to make; and my time was limited. 
Nevertheless I had planned from the first to make direct weighings 
of the central nervous system for very short series of the Norways 
at each of the European stations. This was not done at Vienna 
because specimens for the purpose could not be obtained during 
the period of my stay there, but it was done for both the Paris 
and the London Norways. It is these latter records which are 
now to be considered. The data are given in tables 14 and 15. 
When these data for the weight of the brain and the weight of 
the spinal cord are entered in relation to the corresponding stand- 
ard curves for brain weight based on body weight (Donaldson and 
Hatai, ’11) as given in chart 2, it is plain that both the European 
series closely agree with the respective standards for brain and 
spinal cord. The mean percentage deviation of the values as 
observed, from those of the standards, are given in table 16, A. 
For comparison and control we have also given in table 16, B, 
the mean percentage deviation of the values as observed from 
