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Rh by the addition of either of those substances in excess. With respect to hydrochloric acid, the result was the same as before described.

It cannot appear at all surprising that the areolar tissue of the foetus differs from that of the adult, when it is known that many cell-membranes undergo a change in their chemical constitution at different stages of their development, and that the growth of the cells is not a mere mechanical expansion.

Previous to quitting the subject of areolar tissue, we must consider some other processes, by means of which a new for- mation of it takes place in the adult. If (as I have already laid down as an axiom in my first essays, Froriep’s Notizen, 1838, Nos. 91, 103, and 112) the formation of cells be really the principle of development of all organic structures, it must apply no less to pathological than to physiological processes; and that it really does so, is proved by the investigations of Henle with reference to the new products resulting from inflammation, namely, exudation, suppuration, and granulation; the results of his observations are communicated in Hufeland’s Journal, vol. lxxxvi, No. 5.

Vogel pronounced the pus-corpuscles to be epithelium, in consequence of their resemblance to epithelial cells, and there was much of probability in the statement, so long as it ap- peared that every diversity in the physiological signification of an elementary structure was based upon a recognizable diversity of formation. But this conclusion lost its importance, when I brought forward the formation of cells as the common principle of development of elementary structures, which were perfectly distinct in a physiological sense, and at the same time showed the most opposite tissues to be developed from cells, which, in the first instance, perfectly resemble each other, and present no distinction either in appearance or in the signification of their individual parts. Henle, however, proved a positive difference between the epithelial cells and pus-corpuscles, for he found that the nuclei of the youngest epithelial cells were not broken down by the action of acetic acid like those of the pus-corpuscles. The latter must, therefore, be regarded as peculiar cells, which are developed in the serum | of pus in the same manner that all other cells originate in their cytoblastema; the only difference being that in this