BIOLOGY: H. S. WASHINGTON 
625 
of chlorophyll. Likewise sodium salts are, especially relatively to those 
of potsssium, decidedly toxic toward most vegetable life, though some 
plants, even of the highest genera, have become halophytic and have 
adapted themselves to soils and waters containing relatively large con- 
centrations of sodium salts. Even in these, however, it would appear 
that potassium is the one of the alkali elements necessary to the plant's 
existence. 
Briefly put, therefore, these relations of activity and toxicity of the 
two pairs of salts are antagonistic in the two kingdoms; that which is 
active in metabolism and chiefly necessary for life in the animal being 
relatively toxic in the vegetable, and vice versa. 
Finally it may be pointed out that, according to Reichert,^ hemoglobin 
is entirely absent from the lower orders of animals, such as the protozoa, 
porifera and coelenterata, is rare in the echinodermata, and that chloro- 
phyll is present in some of these, as the protozoa. Thus it might almost 
be suggested that the nearer the animal organism approaches the vege- 
table the less the influence of iron and the greater that of magnesium in 
assimilative metaboHsm. 
The facts thus very briefly and imperfectly set forth seem consistently 
and collectively to lead to the conclusion that, in general, of the four 
elements discussed, iron and sodium are, relatively to the other two, 
jointly necessary to animal metabolism and existence, while, per contra, 
magnesium and potassium replace them as essentials for plant life. 
Here we have, then, though opposed in the two types of organic metab- 
olism, the same congruity between the two pairs of elements that has 
been shown to exist in minerals and igneous magmas. Whether this 
apparent state of affairs is merely coincidental and due to such external 
factors as conditions of environment, or whether it is based on some 
fundamental chemical characters or relations of the elements involved, 
can not be adequately discussed here. 
Thus it might be argued in favor of the first supposition that the pres- 
ence of abundant sodium in the blood plasma is due to the fact that 
this may represent the sea water in which the present day animal's an- 
cestors once lived; that the presence of iron in the blood pigments may 
be ascribed to the existence of this element in two valencies, ferric and 
ferrous iron, and their ready transformation from one state of oxidation 
to the other ;io that the presence of potassium rather than sodium in 
plants may reasonably be connected with the greater resistance to 
decomposition and greater insolubility of the potassimn than the sodium 
minerals, and the consequent greater tendency of the former to accumu- 
late in soils; and, lastly, that the fact that chlorophyll is a magnesium 
