BRAINS OF EUROPEAN AND AMERICAN RATS COMPARED 77 
TECHNIQUE 
In all cases the rats were brought alive to the laboratory, killed 
with chloroform, weighed and the body length taken (see Don- 
aldson, ’09). 
Then, either the central nervous system was removed and 
weighed, according to the usual technique (Donaldson and Hatai, 
11) or the head cut off. This latter was marked with a num- 
bered metal tag and preserved in 60 per cent alcohol, pending the 
preparation of the skull. As all the series were treated in the 
same manner, the effects of the 60 per cent alcohol in modifying 
the capacity of the cranium should be similar, provided of course 
that the composition of the skull bones was also the same. 
The skulls were cleaned by immersion for from 5 to 6 hours at 
a temperature of 90° C. in 100 ee. of a 2 per cent watery solution 
of commercial ‘gold dust washing powder.’! The very young 
skulls required less time and a half strength solution. 
The softened tissues were removed with a bone scraper. The 
skull was then marked with water proof ink, dried in the air, and 
the foramina at the base plugged with a minimal quantity of 
universal cement to prevent the escape of the shot later used for 
determining the cranial capacity. 
To determine the capacity of the dried cranium? it was filled 
with new number eleven shot. These shot are 0.06 of an inch 
in diameter and weigh individually from 0.0203 to 0.0215 grams 
and therefore run from 47 to 49 to the gram, with a mean of 48. 
In filling the cranium the following method was used: The 
cranium was held vertically between the thumb and forefinger of 
the left hand with the ventral side towards the observer. The 
shot was poured from a small aluminum beaker into the cranium 
through the foramen magnum until it was nearly filled, then trans- 
ferring the cranium to the right hand, and holding it vertically 
between the thumb and middle finger with the index finger closing 
1 “Gold dust washing powder’ consists of about 45 per cent sodium carbonate, 
30 per cent soap powder and 25 per cent water. 
2 Departing from the strict anatomical nomenclature, and following the usage 
of the anthropologists, we shall here employ the term ‘‘cranium’’ for the skull 
without the mandible (see Cunningham, ’09, p. 103, note 1). 
