Franklin P. Mall 335 
equals the square root of one hundred times its length from vertex to 
breech in millimeters. Thus an embryo 30 mm. long is \/ 30 X 100, 
or 54 days old. Or, to determine the vertex-breech length of an embryo 
for a given number of days, square the number of days and divide by 
one hundred. Thus the vertex-breech length of an embryo 30 days old is 
— or 9 millimeters. The data upon which this rule rests will be 
found in my paper on the pathology of early human embryos.* This 
formula apples only to embryos up to 100 mm. in length. In embryos 
from 100 to 220 mm. long from vertex to breech the length in milli- 
meters equals the age in days. 
In nearly all instances the embryos were hardened either in alcohol 
or in formalin. Not only is this recorded in my notes, but it is also 
indicated by the condition of the tissue in case the specimen has been cut. 
It is very apparent from all of my specimens, both normal and patho- 
logical, that when the embryo is macerated to the least degree the 
effect is much more marked in the brain than elsewhere It appears 
that any dissociating fluid effects the brain first. So in order to tabu- 
late the specimens I have had to express the extent of maceration of 
the brain in degrees, which in general is two or three degrees more ad- 
vanced than that of any other organ of the embryo. 
The condition of the brain is marked 0 in the table in case its lateral 
mesial surfaces are perfectly smooth as pictured by Retzius for the fresh 
brain of a human.embryo at the end of the third month. Those brains 
in which there are slight irregularities of the walls, as is the case when 
there is some shrinkage with separation of the vesicle, are marked 1. 
Some of these folds are certainly not true transitory fissures, for in the 
same embryos there is the same separation of the epithelial cells in the 
oesophagus and in the intestine. I have, however, included in this 
group those brains in which the transitory fissures are just beginning. 
The brain is marked 2 whenever it has the typical transitory fissures 
as usually described. In case the infolding is more extended, showing 
signs of maceration and disintegration of the walls of the brain with 
loose cells within the ventricle, it is marked 3. When the maceration 
has gone so far that the vesicles are filled with cells and the brain is 
nearly solid, it is marked 4. In the specimens marked 1 to 4 the spinal 
3 Mall, Johns Hopkins Hospital Reports, IX, 1900. 
4 The condition of specimens marked 1 equals about those with the least number 
of fissures as pictured by Retzius on Plate 1 in his great monograph, Das Menschen- 
hirn. Those marked 2 represent those figures on this same plate with the greatest 
number of fissures. 
