No. 1.] ORIGIN OF HUMAN MONSTERS. 29 
I.5 per cent aqueous solution of potassium chloride shortly 
after fertilization. He found that the eggs develop in a pretty 
normal fashion with the exception that though the heart de- 
velops it does not beat at all. The blood-vessels develop prop- 
erly as regards their course and division, but their lumina are 
irregular, like a chain of beads, which Loeb believes to be 
due to a lack of normal blood-pressure. Similar pictures 
may be seen in pathological human embryos, that is, only part 
of the vascular system is present, or the heart is atrophic but 
some of the blood-vessels are present, or the whole vascular 
system of the body is absent, with remnants of vessels in 
the yolk sac and in the chorion. In the last instance the 
vessels of the body may have been present at one time, for 
they should not have reached the chorion without passing 
first through the body. The embryos in Loeb’s experiments 
rarely hatched, and all of them died before the sixteenth day, 
due to heart poisoning. Loeb thought that all of the organs— 
brain, eye, ear and myotomes—developed without any marked 
anomalies, but I do not think that his experiments were ex- 
tensive enough to test this point thoroughly. However, he 
states that the pigmentation of the yolk sac was affected 
decidedly by the absence of the circulation. Under normal 
conditions the pigment, which is at first evenly scattered over 
the yolk, wanders to the blood-vessels as soon as the circu- 
lation begins and stays there, forming pictures which corre- 
spond with the branching vessels. In potassium embryos where 
the blood does not circulate the pigment cells are not attracted 
to the blood-vessels, but remain scattered evenly over the 
yolk. 
By extirpating the heart anlage from very young frog em- 
bryos Knower® obtained a similar arrest in the development, 
but his experiments show that absence of the heart or early 
defects in its action produces marked abnormalities in the de- 
velopment of the embryos. While the earlier stages of the 
development of these frog embryos is normal, the later changes 
®Knower, Anatomical Record, Amer. Jour. Anat., VII, 1907. 
