If we try to analyse such results as Fischer’s from a physico­chemical point of view, we must realize that what we call life consists of a series of chemical reac­tions, which are connected in a catenary way; inasmuch as one reac­tion or group of reac­tions (a) (e. g., hydrolyses) causes or furnishes the material for a second reac­tion or group of reac­tions (b) (e. g., oxida­tions). We know that the temperature coefficient for physio­logical processes varies slightly at various parts of the scale; as a rule it is higher near 0° and lower near 30°. But we know also that the temperature coefficients do not vary equally for the various physio­logical processes. It is, therefore, to be expected that the temperature coefficients for the group of reac­tions of the type (a) will not be identical through the whole scale with the temperature coefficients for the reac­tions of the type (b). If therefore a certain substance is formed at the normal temperature of the animal in such quantities as are needed for the catenary reac­tion (b), it is not to be expected that this same perfect balance will be maintained for extremely high or extremely low temperatures; it is more probable that one group of reac­tions will exceed the other and thus produce aberrant chemical effects, which may underlie the colour aberra­tions observed by Fischer and other experi­menters.

It is important to notice that Fischer was also able to produce aberra­tions through the applica­tion of narcotics. Wolfgang Ostwald has produced experimentally, through varia­tion of temperature, dimorphism of form in Daphnia.

5. Next or equal in importance with the temperature is the nature of the medium in which the cells are living.

It has often been pointed out that the marine animals and the cells of the body of metazoic animals are surrounded by a medium of similar constitu­tion, the sea water and the blood or lymph, both media being salt solu­tions differing in concentra­tion but containing the three salts NaCl, KCl, and CaCl2 in about the same relative concentra­tion, namely 100 molecules NaCl : 2.2 molecules of KCl : 1.5 molecules of CaCl2. This has suggested to some authors the poetical dream that our home was once the ocean, but we cannot test the idea since unfortunately we cannot experi­ment with the past. Plants, unicellular fresh-water algæ, and bacteria do not demand such a medium for their existence.

Herbst had shown that when sea-urchin larvæ were raised in a medium in which only one of the constituents of the sea water was lacking (not only NaCl, KCl, or CaCl2, but also Na2SO4, NaHCO3, or Na2HPO4), the eggs could not develop into plutei; from which he concluded that every constituent of the sea water was necessary. This would indicate a case of extreme adapta­tion to all the minutiæ of the external medium.

Experiments on a much more favourable animal for this purpose, namely, the eggs of the marine fish Fundulus, gave altogether different results. The eggs of this marine fish develop naturally in sea water but they develop just as well in fresh or in distilled water, and the young fish when they are made to hatch in distilled water will continue to live in this medium. This proves that these eggs require none of the salts of the sea water for their development. When these eggs are put immediately after fertiliza­tion into a pure solu­tion of NaCl of that concentra­tion in which this salt exists in the sea water practically all the eggs die without forming an embryo; but if a small quantity of CaCl2 is added every egg is able to form one, and these embryos will develop into fish and the latter will hatch. This led the writer to the conclusion that these fish (and perhaps marine animals in general) need the Ca of the sea water only to counteract the injurious effects which a pure NaCl solu­tion has if it is present in too high a concentra­tion.[261] When we raise the eggs in a pure NaCl solu­tion of a concentra­tion ≦m/8 practically every egg will develop; and even in a m/4 or 3⁄8 m many or some eggs will form embryos without adding Ca; it may be that a trace of Ca present in the membrane of the egg may suffice to counter-balance the injurious action of a weak salt solu­tion.

The concentra­tion of the NaCl in the sea water at Woods Hole (where these experi­ments were made) is about m/2, and as soon as this concentra­tion of NaCl is reached the eggs are all killed as a rule before they can form an embryo, unless a small but definite amount of Ca is added. It was found that the eggs can be raised in much higher concentra­tions of NaCl, but in that case more Ca must be added. The following table gives the minimal amount of CaCl2 which must be added in order to allow fifty per cent. of the eggs to form embryos. (The eggs were put into the solu­tion an hour or two after fertiliza­tion.)

TABLE XVI

Concentration
of NaCl		Cc. m/16 CaCl2 Required
for 50 c.c. NaCl Solution
m.
3⁄8  0.1
4⁄8  0.3
5⁄8  0.5
6⁄8  0.6
7⁄8  0.9
8⁄8  1.2–1.4
9⁄8  1.8–2.0
10⁄8  2.0–2.5
11⁄8  2.0?
12⁄8  3.0–3.5
13⁄8  6.0