442 
PHYSIOLOGY: J. LOEB 
decision was made, as in the very weak as well as in the strong solutions 
the larvae fall first to the bottom and will not rise until after some hours. 
Other experiments gave similar results. 
If we select for comparison the experiments with the moderate con- 
centrations (between m/8 and m/2 NaCl + KCl) we find that the value of 
C'Na + K/^Mg + Ca ^^^^'^-^ 1^^^^ aroufid 35.0 or in other words that the 
concentration of CaCl + MgCl required increases in direct proportion 
with the concentration of NaCl + KCl; as far as the degree of accuracy 
of these experiments permits it to be stated. In concentrations above 
m/2 NaCl the animals will usually not all rise or if they do they soon fall 
to the ground again and this makes the determinations of the endpoint 
difficult. The value of MgCl2 + CaCL to be added to m/16 NaCl is 
higher than the theory demands and therefore the law does not hold 
strictly in this case. The law of direct proportionality found for moderate 
concentrations is therefore Weber^s law. As is well known, Weber's law 
TABLE II 
Maximal Amount of CaCl2 + MgCh Which Allows the Larvae to Swim in 50 cc. 
(NaCl + KCl) OF THE Following Concentrations 
CONCENTRATION 
NaCl + KCl 
MAXIMAL AMOUNT 
CaCh + MgCl2 
OF 
VALUE OF 
^Na + K 
^Mg + Ca 
50 CC. m/16 NaCl + KCl 
> 5 
cc. 3/8 m CaCl2 
+ MgCl2 
1.67 
50 cc. m/8 NaCl + KCl 
> 8 
cc. 3/8 m CaCla 
+ MgCl, 
2.08 
50 cc. m/4 NaCl + KCl 
>14 
cc. 3/8 m CaCl2 
+ MgCl2 
2.38 
50 cc. m/2 NaCl + KCl 
>25 
cc. 3/8 m CaCla 
+ MgCl2 
2.67 
i s not strictly correct for very low or very high intensities and the devi- 
ation is in the same sense as in our experiments, namely as if the weakest 
concentration tried were stronger than it actually is. 
5. According to the writer's theory the swimming motions should also 
cease when the value of C^a + K/^Mg + Ca f 2.11s below a certain limit. It 
is more difficult to determine this endpoint than the other one, since 
with an increasing concentration of Ca + Mg the percentage of the 
larvae able to swim diminishes very gradually. 
When the larvae are put into solutions with an excess of CaCl2 + 
MgCl2 they all swim at first but in a few minutes they fall to the bottom 
though they will live for a long time. The power of rising to the sur- 
face and forming a permanent dense helio tropic cluster no longer existed 
when more than the following quantities of 3/8 m CaCl2 + MgCl2 
were added to 50 cc. of NaCl -f KCl (Table II). The final observations 
were usually taken after two days. 
