THEIR LIFE AND AFFINITY. 251 
in a continual change of matter in the parts already formed (the vege- 
tative as well as the higher and properly animal parts), lives absolutely 
the life of the plant. We likewise observe, that here also the fluid 
parts are the sources from which the several solid parts are formed by 
different attractive affinities, for this reason, that the external nourish- 
ing substances first enter into the fluids, but at the same time the se- 
cretions which are given off from the fluid parts of the body are carried 
away in the form of liquids, vapours, or gases. However, to perform 
this attraction and repulsion, one condition is requisite which is equally 
necessary in the life of plants, and that is the circulation of the fluids. 
This circulation we have seen performed in the plant through the 
polarity between the root and the flower, and therefore in a linear di- 
rection from one end to the other. But since the animal is a plant the 
root of which is turned inwards, a similar motion of the fluids, from 
the absorbing to the exhaling pole, instead of being directed linearly 
from one extremity of the body to the other, must take a centrifugal 
and centripetal direction, inasmuch as it is but an action and reaction 
between external and internal organs. We have observed that the cir- 
culation of the fluids in the embryo is between the embryo as a centre 
and the integuments of the egg as the periphery; and that the circula- 
tion is not confined to the embryo itself until it has attained its full 
maturity *, at which period it is observed alternating between the heart 
(as the centre of vegetation) and the periphery; and in the higher ani- 
mals and man, partly toward the whole bodily structure and its common 
integument the epidermis, partly toward the epidermis turned inwards 
in the organ of respiration, and vice versd. Hence it follows that this 
movement of the sap or blood is not properly a circular motion, and 
has therefore no true resemblance to the rotatory motion of the hea- 
venly bodies ; because these have an intermediate movement which is 
the result of attraction and repulsion; whereas the movement of the 
blood appears as an alternation of attraction and repulsion, which is 
most analogous to the ascending and descending movement of the sap 
inthe plant. This also leads to the conclusion that both this movement 
and its direction are originally the mere effect of the polar attraction 
and repulsion of the fluid itself. Wherefore this circulation may take 
place without needing any other mechanical aid, as for instance the 
pressure of the vascular surfaces, of which aid many animals are for the 
most part destitute. Indeed, the original unimportance of such aids is 
rendered fully evident by the fact that the vessels, like all other solid 
parts, are formed only by the circulating fluids,—consequently, that 
* The essential difference between the earliest and the later form of the cir- 
culation in the egg during the process of incubation has been recently demon- 
strated in the beautiful experiments of Pander. 
