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ANATOMY: H. H. DONALDSON 
Again, the submature or mature main valleys, profile 2', or the prentcyclees 
presumably excavated beneath the wide-open old valleys of the earlier cycle, 
have not as yet encroached greatly upon the ore-bearing part of the inter- 
valley highlands, profile 6. The encroachment and removal will be greater and 
greater as the main valleys of the present cycle are widened, profile 3', (the 
recent submergence is not indicated here) and as branch valleys are extended 
headward into the highland by retrogressive erosion. Still later, profile 4', 
the highland surfaces of the earlier cycle and their residual laterite cover will 
be completely worn away; but finally, when old age is again approaching, 
profiles 5' and 6', new deposits will again be formed by rock disintegration and 
ore concentration on the subdued and lowering inter-valley hills of the future, 
just as happened in the past. 
The superficial laterite ores of the serpentine highlands in New Caledonia 
therefore seem to be local as to area of development and intermittent as to 
time of origin and duration of occurrence. The same relations presumably 
obtain in a general way regarding the limonite and bauxite deposits of our 
Appalachian valleys. 
1 Report, Ontario Bureau Mines, No. 26, part 1, 1917. 
2 Richesses minerales de la Nouvelle Caledonie, Ann. des Mines, 1903-04. 
A COMPARISON OF GROWTH CHANGES IN THE NERVOUS SYS- 
TEM OF THE RAT WITH CORRESPONDING CHANGES 
IN THE NERVOUS SYSTEM OF MAN 
By Henry H. Donaldson 
Wistar Institute of Anatomy and Biology, Philadelphia 
Read before the Academy, April 23, 1918 
For a number of years the albino rat has been used for the study of growth 
changes which occur in the brain between birth and maturity. 
As occasion offered, the results obtained from the rat have been compared 
with those from man, in order to determine how far the rat might be used for 
the study of the corresponding problems in man. 
As all of these studies were in the field of growth, and as growth is a function 
of age, it became necessary in order to make the cross reference, to determine 
the equivalent ages of the rat and man. 
Two observations were available for this determination. 
1. The rat doubles its birth weight in 6 days, while man takes 180 days — 
giving a ratio of 1 to 30 days. From this it would appear that the rat was 
living 30 times as fast as man. 
2. Again, a rat of 3 years is very old — so that I have ventured to compare a 
rat of this age with a man of 90 years. Once more the rat appears to be living 
30 times as fast as man. 
