86 HENRY H. DONALDSON 
The average of the deviations as given in tables 16, A and 16, 
B, is the figure used in the subsequent discussion. 
According to these determinations, it is plain that both the 
Paris and London Norways have central nervous systems (brain 
and spinal cord) slightly heavier than that of the standard Phila- 
delphia Norways. The deviations of the European forms from 
the standard are so small however, even in the case of the Paris 
series, that they are probably not significant. It is possible to 
conclude therefore that the Paris and London rats do not have 
central nervous systems of less relative weight than those found in 
the Philadelphia Norways, while as the records stand, the relative 
weight is really slightly higher. Although, as has been explained, 
the corresponding data for the Vienna Norways are lacking, we 
shall see further on that the true cranial capacity of the Vienna 
Norways is compatible with a brain weight about equal to that of 
the Philadelphia series or a trifle below it—but probably not 
deviating to any significant degree. 
Although the data for the percentage of water in the brain and 
spinal cord are not presented here because the determinations 
could not be made abroad with all the desired precautions, yet the 
data as they stand agree well with those for the American Norway 
as previously determined (Donaldson and Hatai, *11). In this 
respect then the European and American Norways are again in 
agreement. 
The foregoing determinations are highly important for the 
control and interpretation of the data on cranial capacity since 
these latter, as we shall see, cannot be taken at their face value, 
but must be corrected for shrinkage, which varies not only accord- 
ing to age, but also according to other less evident conditions. 
The characters of these crania, so far as they are indicated by 
weight, have been discussed elsewhere (Donaldson ’12). 
CRANIAL CAPACITY 
In determining the cranial capacity by the methods given earlier 
we obtain in the first instance the weight of the shot necessary to 
fill the cranium. It was found that one cubic centimeter of the 
