ANTHROPOLOGY: A. E. JENKS 
165 
Pigmentation is due to pigment metabolism. In 'complete albinism' pig- 
ment metabolism completely fails to start. In 'incomplete albinism' pig- 
ment metabolism occurs only incompletely. In 'partial or imperfect albi- 
nism' pigment metabolism locally fails or never starts. In ' progressive al- 
binism,' or dynamic leucosis, pigment metabolism, though having apparently 
once started at some time, fails in certain areas. 
Before giving proofs of progressive albinism as shown by the recent 
research, let me add another quotation from the original study which 
states two of the live problems then left open for further investigation: 
2. Whether the albinistic areas extend their borders after once having been 
known, or whether there is, instead, a progressive failure of pigment metabo- 
lism within a definite area.^ 
3. Whether an at-one-time albinistic area ever revives within itself the proc- 
ess of pigment metabolism.-'' 
Problem number 2 has been solved. There is an extension of the 
albinistic areas. 
Problem number 3 has also been solved, and its solution is surprising. 
There is a revival of the process of pigment metabolism within an at- 
one-time albinistic area. 
The process followed in the study of the two problems (numbers 2 
and 3 above) follows. 
Two negatives of the same individual were made as early as possi- 
ble from the same points of view. The second negative was taken fol- 
lowing a lapse of six months after the making of the first negative. The 
two negatives were measured by Mr. H. B. Wilcox,' Scholar in Astron- 
omy at the University of Minnesota. The measurements were made 
on the Repsold photographic-plate measuring machine owned by the 
Department of Astronomy, University of Minnesota. Two lenses (one 
of 30 diameters, and one of 10 diameters) were used in the measure- 
ments of the distance "C" shown on Plate I. It is the horizontal meas- 
urement across the albinistic spot enclosing the navel. All subsequent 
measurements were made by use of the lower, or 10-diameter lens, be- 
cause it resulted in better definition. However, the accuracy of the 
measurements by the 10-diameter lens is well confirmed by the one 
duplicate measure made by the 30- diameter lens, since the results ob- 
tained by the two lenses agree within the limits of error. 
The error indicated is based on the theory of Least Squares — the 
theory of error universally employed in measurements of stellar photo- 
graphs. However, attention should be called to the possibility of sys- 
tematic error. This possibility of systematic error is, nevertheless, not 
