Porter — The Growth of St. Lowis Children. 347 
that frequent weighing is the most practical and on the whole 
the most certain method of detecting the presence of influences 
that are working injury to the development of the child. 
The skillful breeder of cattle depends on systematic weighing 
to inform him if his efforts are meeting with success, but 
children are left to grow at haphazard. 
It is not enough that overstrain should be recognized by the 
harm it has done. The child should be guarded against the 
possibility of harm. The anthropometrical system proposed 
offers a means of doing this. It infallibly discovers 
the children whose physical development is below the 
standard of their age. It no less certainly indicates the 
physical development which most often accompanies the 
power to do the mental work of any grade. It therefore 
divides the pupils into two bodies; those physically compe- 
tent and those physically incompetent for a clearly defined 
degree of mental exertion. When working with great num- 
bers, the infallibility of this system is practically absolute and 
theoretically almost absolute. When applied to individuals, 
errors will certainly occur, but the number of errors will 
according to the laws of probability be less than the number 
of correct conclusions, and these errors cannot influence the 
great fact that such a system is competent to call attention to 
the children who will probably be unable to do the normal 
work of their age without injury. Each individual case must 
then be treated on its own merits. 
The proposed system of physica] examination requires: — 
I. The collection of sufficiently extensive data by the gen- 
eralizing method. 
II. The determination of the means and the probable 
deviations of height, weight, girth of chest, strength of 
Squeeze, etc., for each age. 
III. The division of the individuals at each age into groups 
in terms of the probable deviation from the mean height, as 
illustrated above, and the calculation of the mean and prob- 
able deviation of the weight, girth of chest, etc., of each 
group. 
IV. The determination of the mean physical development 
of the pupils in each class or grade of the school system. 
