536 STUDIES IN GENERAL PHYSIOLOGY 
The concentration with which we have to deal in this case 
is, according to him, 0.04 per cent. instead of 0.026 per cent. 
of the serum. So far as the rhythmical contractions of the 
muscle are concerned, the claim of Greene is incorrect. 
When a muscle does not contract rhythmically in a NaCl 
solution containing Ca, when the concentration of the CaCl 
solution is 0.026 per cent., then no contractions occur at all 
at a concentration of 0.04 per cent., or higher. For the 
apex of the heart the relations are no different, and the claim 
of Greene to the contrary rests, so far as I can see from his 
paper, upon a misunderstanding. 
In observing the “stimulating” effect of the 0.04 per 
cent. CaCl, solution the strip of heart muscle did not lie in 
such solution, but hung in a moist chamber, and was moistened 
with two or three drops of the CaCl, solution named. It 
then began to beat rhythmically. If we assume that cal- 
cium did indeed have something to do with this, we are still 
not dealing in this case with the same condition of affairs 
that we have when heart muscle is immersed in a large quan- 
tity, about 100 to 200 c.c., of such solution. In the latter 
case a larger number of Ca ions would enter the muscle in 
the unit of time. By moistening the muscle with two or 
three drops of a 0.7 per cent. NaCl solution containing 
0.04 per cent. CaCl, the larger amount of the fluid runs off, 
and the few Ca ions which enter the muscle are perhaps in 
actual number equal to those which enter from a NaCl solu- 
tion containing a very small amount, say 0.001 per cent. 
CaCl,. Greene and Howell have overlooked the fact that 
the concentration of the solution is not the determining 
factor in the latter case, but the number of molecules which 
are driven into the muscle (through osmotic pressure). 
When it is found that 100 c.c. of morphine of a certain 
concentration kill a dog, and when it is further observed 
that yy ¢¢. 0° A morphine solution two or three times as 
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