PuHYSIOLOGIOAL Erreots or Lack oF OxyGen 421 
The black and red pigment cells can be distinguished 
from each other, not only by their color, but also by their 
form. The latter send out a large number of thin pseudo- 
podia-like processes which are never found in the black pig- 
ment cells. In the experiments on the effect of lack of 
oxygen on the cardiac activity of the Fundulus embryo, it 
was noticed that the originally dark yolk-sac gradually be- 
came lighter in color when exposed to hydrogen for a long 
time. The pigment cells can be observed very carefully 
with the microscope, and I expected to observe the same 
phenomena that Biedermann observed in frogs. This was, 
however, not the case. It was found in the course of a series 
of experiments that the dark pigment granules and the 
black cells gradually disappear the longer the current of 
hydrogen is kept up, and that the collection of the pigment 
in the center of the cell does not occur. 
The changes in the red pigment cells in lack of oxygen 
are of a somewhat different nature. The lightening of the 
color often occurs in this case also. Besides this, however, 
the cells become smaller. The tips of the cell-processes 
break off, remaining visible at first as tiny droplets, which 
disappear later. As this process continues, the pigment 
cells gradually become smaller. 
These changes remind one of the fact that certain dyes 
become colorless when reduced. In our experiments it 
might also be possible that the discoloration of the black 
pigment is a result of a reduction, which does not occur in 
the presence of atmospheric oxygen. 
XIII. CONCLUDING REMARKS 
It seems to me that the most important result of the 
foregoing experiments consists in the proof which has been 
brought forward that in certain cases at first molecular, 
and later morphological, changes are brought about in cells 
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