1263 
of lecithine-soles, is almost entirely neutralized by a definite con- 
centration of Ca’-ions. 
The surface-tension of a pure 1°/, lecithine-sole amounted to 
75.9.*) 
Consequently it appears from this table that the influence of a 
definite concentration of an unbalanced NaCl-solution on the surface- 
tension of a lecithine-sole, may be neutralized almost entirely by 
the addition of Ca-ions, but it appears at the same time that only 
one definite [Ca”] can do this and that this balancing effect can be 
produced neither by a too large [Ca“] nor by a too small one. The 
degree of this balancing [Ca’] depends on the ion-system present. 
How we should explain this balancing is not known with certainty ; 
it seems that LorB*) and others have modified the theory of the 
electro-chemical ion-proteid-compound in favour of an ousting from 
the surface. In a biological respect examples have of late come to 
our knowledge from which it appears that also with the physiolo- 
gical ion-balancing the degree of [Ca“] is decisive, and that very 
slight fluctuations of these [Ca”| may have an important physiolo- 
gical consequence. *) 
It may be understood therefore that these [Ca”] should be kept 
constant in the blood-plasm, as well as, e.g. the [H']. The buffer- 
system by which this is principally effected has been indicated 
by Rona and Takanasni*). According to these authors there is 
for the free calcium-ion-concentration in the blood the equation: 
Ke Ne Sn (K being about 350), a relation we could entirely 
L 
confirm by direct measurement of the [Ca”|.®) As the [H'] practi- 
cally varies very little in physiological and also in pathological 
cases, the |[Ca”] will consequently be controlled chiefly by the con- 
centration of the bicarbonate-ions. An increase of the [Ca”] will 
depend in the first place on a decrease of the [HCO’,], in other 
words of an acidosis. 
The main object of this communication is what influence the [Ca™] 
and its fluctuations have on the irritability of the N. vagus. As a 
1) Measured with the stalagmometer of TRaAuBE: Handbuch der Biochemische 
Arbeitsmethoden V, Bd. 2. 1912. 
2) LoeB: Journal of General Physiology, Vol. I en II. 
8) HAMBURGER en BRINKMAN : Biochemische Zeitschrift 88, 97, 1918; 
BRINKMAN: Biochem. Zeitschr. 95, 101, 1919. 
4) Rona en TAKAHASHI: Biochemische Zeitschrift 49, 370, 1913. 
5) BRINKMAN and miss vAN Dam, Verslagen Kon. Akad. v. Wetenschappen, 
meeting of 25 Oct. 1919. 
