284 Periodicity of the Organic World : [May, 
to marine, or at least aquatic, forms of life. On the other 
hand, the only element which rank in the first series, 
hydrogen, is essential to all living beings ; so are three at 
least of the second series : carbon, nitrogen, and oxygen , 
whilst fluorine, which also belongs to this series, is met 
with in the skeletons of all the higher animals. All. the 
elements of the third series, to wit sodium, magnesium, 
aluminium (rarely), silicon, phosphorus, sulphur, and chloiine, 
enter into the structure of organisms. In the fourth seiies 
are the important elements of potassium and calcium, man- 
ganese, very widely present in plants, iron, and nickel, 
which, though it has not yet been demonstrated as present 
in any plant or animal, yet plays an important part in the 
pseudo-organisms produced by M. G. Fournier and by 
MM. Monnier and Vogt. 
On the other hand, none of the elements forming the 6th, 
8th, 9th, 10th, nth, and 12th series of the classification 
enter into organic beings. 
The first reply to any considerations founded upon this 
faCt is that the “ organic elements ” above enumerated are 
merely a synonym for the commoner elements. Were 
baryta, for instance, as plentiful as lime, it also might be 
found in the tissues of plants and animals. At the same 
time it must be remembered that in the experiments of MM. 
Monnier and Vogt barium and strontium saccharates, un- 
like the corresponding calcium salt, did not lend themselves 
to the production of organic forms. It may be said that 
barium is highly poisonous. True, but strontium is not. The 
question further remains whether it is a mere matter of acci- 
dent that the commoner elements, those holding the posi- 
tions first mentioned, should exclusively enter into the 
structure of plants and animals ? Perhaps those elements 
whose atomic weights are above that of iron ( = 56) havetaken 
a line of development which withdraws them from the play 
of those agencies which constitute life. If we look at the 
series of atomic weights we find that all the elements from 
carbon onwards to calcium, having respectively the atomic 
weights 12, 14, 16, 19, 23, 24, 27, 28, 31, 32, 35*5, 39> 4°> are 
organisable, if we may use the term. Below this group we 
have only hydrogen (= 1), and above it merely manganese 
(55), iron (56), copper (63), zinc (65), bromine (80), and 
iodine (127). So that of the twenty organisable elements 
thirteen, or in round numbers two-thirds, have atomic 
weights situate between 12 and 40. This faCt surely indi- 
cates that with higher atomic weights organisation becomes 
more difficult. 
