RHYTHMICAL CONTRACTIONS IN MUSCLE 585 
able to beat rhythmically in the serum of blood containing 
Ca. Greene has recently shown that when CaCl, is added 
to a physiological NaCl solution in a concentration equal to 
that in which it exists in the serum, the pulsations of the 
ventricle cease, while rhythmical irritability continues. That 
is the same behavior, therefore, as is the case with the 
rhythmical contractions of the gastrocnemius, and we may 
therefore assume that for the heart-beat the same circum- 
stances come into consideration as for the rhythmical con- 
tractions of skeletal muscle; with the exception, of course, 
of the conditions for the conduction of the stimulus which 
we have discussed under paragraph 2. The réle of the 
hydroxyl ions for the heart activity might also be the same 
as that we have found to be the case for the rhythmical con- 
tractions of skeletal muscle.’ The further we carry the 
analysis of the two processes, the more complete, I believe, 
we shall find their identity, with the exception, of course, of 
the conditions of conductivity of the stimulus. I find only 
two contradictory facts. One is originated by Howell—that 
NaCl is only of osmotic significance in the activity of the 
heart. So far as the ventricle is concerned, this statement 
of Howell’s is contradicted by the observations of Aubert. 
The second assertion comes from Howell’s pupil, Greene.’ 
Greene has observed very correctly that CaCl, in the same 
concentration as it exists in the serum prevents the rhythmi- 
cal contractions of the ventricle. Then, however, he adds 
the following assertion, that “when the amount of CaCl, in 
the serum is slightly increased, regular contraction begins.” 
1 have recently tried to determine how many free hydroxy] ions the blood con- 
tains in the unit volume. I find that it cannot possibly be more, and is probably 
less, than those present in the same volume of a one-thousandth normal NaOH solu- 
tion. Until now we have always made the alkalinity determination of the blood by 
titration. For the specific alkalinity of the blood, however, only the active alkalin- 
ity—that is, the concentration of the free hydroxyl ions in the blood—comes into 
consideration. It has since been found by Friedenthal, Fraenckel, Farkas, and 
Hoeber that blood has a neutral reaction. [1904] 
2GREENE, American Journal of Physiology, Vol. ITI (1898). 
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