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 embiyo 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 versa. 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 

 in the 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 tdke 

 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. 



