PHYSIOLOGY: /. LOEB 
443 
Considering the difficulty in getting a sharp endpoint, these values are 
in good agreement with Weber's law of proportionality. It is, there- 
fore, apparent that the upper Hmit of the value CNa + K/^Mg + Ca> which 
just annihilates the power of free swimming motions, remains also 
approximately constant, namely about 2, if the value of C^a + K varies. 
Attention should be called to the fact that this value seems to rise 
slowly with the concentration of NaCl + KCl. 
6. It is occasionally stated that the bivalent cations are the stimulat- 
ing ions. This can be disproved if we prepare solutions of MgCl2 + 
CaCl2 in m/2 cane sugar or m/2 glycerine. It is impossible to induce 
the larvae to swim in such solutions. Neither can we induce them to 
swim if we add NaCl -{- KCl to a m/2 cane sugar or glycerine solution. 
This is in harmony with the law that the normal activity is only pos- 
sible if the value of the quotient CNa-i-K/^Mg + Ca keeps within certain 
limits, but contradicts the idea that Ca or Mg stimulate the animals 
into activity. 
7. It has been stated that in a m/2 solution of NaCl + KCl -f CaCl2, 
in the normal proportions, none or few of the larvae can swim, but that 
on addition of either more CaCl2 or MgCl2 or both the larvae will swim. 
We can bring about the same effect if we add instead of MgCl2 or more 
CaCl2 simply some alkali, e.g., 0.8 cc. N/100 NaOH or 0.5 cc. m/10 
NaHCOs to 50 cc. of the solution of NaCl + KCl + CaCls. The larvae 
will after some time rise to the surface and gather permanently in a cluster 
although no MgCl2 is present. This fact brings these phenomena into 
a close parallel with the phenomena of fertilization. I have shown 
that the eggs of sea urchins and other marine animals cannot be 
fertilized in a mixture of NaCl -f KCl although the sperm remains 
active for a long time in such a solution; that the addition of CaCl2 
allows the fertiHzation of a few eggs, but that the addition of either 
MgCl2 or NaOH (or NaHCOs) may allow all the eggs to be fertilized.^ 
This is mentioned to indicate that the phenomena discussed in this 
paper are of a wide biological application. 
Summary. I had formerly shown that the normal functions of an 
organism are only possible if the value C^a+K/^'Mg + ca remains with 
certain limits A and B. In this paper this value has been investi- 
gated in an animal which stands wide variations of C^a+K ^.nd it 
was found that the values A and B remain approximately constant if 
^Na + K changes. This fact is the expression of the Weber- Fechner 
law. Since this law underlies many phenomena of stimulation it ap- 
pears possible that changes in the concentration of antagonistic ions 
