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PHYSIOLOGY: J. LOEB 
for C^a + K can be considered and hence only the lower and upper limit 
for C^g + ca can be determined for this value. A few organisms can 
stand wide variations of osmotic pressure and hence in their case the 
value C^a + K can undergo wide variations. The question arises: How 
do the minimal and maximal values of + ca change when C^a + K 
varies? It is this question which will be discussed in this paper. 
2. The animals used in these experiments were the newly hatched 
larvae of a barnacle {Balanus iherneus) . These larvae upon hatching are 
positively heliotropic and form a dense cluster on the light side of the 
aquarium, so that they can be collected in a pipette with comparatively 
little sea water. They are able to live not only in normal sea water but 
also in sea water which is diluted with eight times its volume of distilled 
water, as well as in sea water whose concentration is raised almost 
50%. 
When such larvae are put into a mixture of NaCl, KCl and CaCl2 
of the concentration and proportion of sea water, the majority will not 
swim but fall to the bottom of the dish. If, however, we increase the 
amount of CaCl2 in the solution the larvae instead of falling to the bottom 
will swim, as they would in normal sea water, and will collect at the side 
of the dish nearest to or most remote from the light. Instead of adding 
more CaCl2 we may add MgCl2 or SrCl2. 
3. If the bivalent cations contained in the solution are of one kind 
only, namely either CaCl2 or MgCl2 or SrCl2, and if they are in sufficient 
concentration to allow the animals to swim, the latter will do so as a rule 
only for about five minutes. If we wish the animals to swim permanently 
we must add a mixture of two bivalent cations, e.g., Ca and Mg. 
In the following experiments a mixture of CaCl2 and MgCl2 was 
always used to supply the bivalent cations. This mixture contained 
the two cations in that ratio in which they occur in the sea water, namely 
1.5 molecules of CaCl2 to 11.6 molecules of MgCl2. The concentration 
of the mixture used was f grammolecular. 
4. When we put the animals into a mixture of 50 cc. NaCl + KCl 
(no matter what concentration) they will fall to the bottom and are 
unable to make sufficiently vigorous swimming motions, although they 
may live in such a solution for a day or longer. Various concentrations 
of the mixture of NaCl + KCl (in the proportion in which these salts 
exist in the sea water) were prepared and it was ascertained what was 
the minimum amount of CaCl2 + MgCU necessary to induce all (or 
practically all) the animals to make normal sv^^imming movements and 
to collect in a dense cluster at the window side (or the opposite side) 
at the surface of the dish. 
