298 STUDIES IN GENERAL PHYSIOLOGY 
whole was markedly retarded in this concentrated salt solu- 
tion, so that a definite judgment of the vascular system could 
be made only so far as the main stems and their branches 
were concerned. These main stems corresponded with the 
main stems of the normal embryo. Yet I was never able to 
discover even the slightest evidence of a heart-beat, much 
less a circulation. The lack of hydrostatic pressure within 
the vessels was particularly evident here from the irregularity 
in the diameter of the blood-vessels; nevertheless, a large 
number of branches, which gradually decreased in caliber, 
sprang from the main vessels. In this case, therefore, tt is 
unquestionably true that the process of branching and the 
growth of the blood-vessels are independent of blood-pres- 
sure. 
4. The experiments with weak KCl solutions also deserve 
mention. In a series of experiments I added 0.25 to 0.5 g. 
to 100 c.c. of sea-water; normal development occurred in 
these solutions. The heart-beat and the circulation 
developed apparently normally. The control eggs, which 
had been taken from the same culture, but raised in normal 
sea-water, completed their development in twelve to sixteen 
days, when the embryos hatched. They lived some four to 
six weeks after escaping from the egg. In the two KCl 
solutions, however, but one embryo, which lived for a day, 
hatched on the twelfth day in the 0.5 per cent. KCl solution. 
All the remaining embryos died between the twelfth and 
sixteenth day. Death unquestionably resulted from a 
poisoning of the heart, and not from a general intoxication. 
5. The experiments cited above show that a KC! solution 
of a definite constitution is the more poisonous the older the 
embryo. One might think that the chemical constitution of 
the individual elements of the heart changes with develop- 
ment; but how can we harmonize with this the fact, which 
has been mentioned above, that the heart of a four-to-five- 
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