CELLS. 45 



to which they are exposed, which pressure is to be referred upon 

 the one hand to the force of the blood, on the other to an 

 attractive force exercised by the cells themselves in absorbing 

 the substances, and to the elasticity of the cell-membranes. 



The excreted matters in general no longer continue in the 

 organism, but are completely removed as in the glands ; in 

 a few localities they remain, taking a solid form, as extra- 

 cellular substance, outside the cells, and form the genuine 

 membrance propria of the glands (e. g. of the renal canals), the 

 proper envelope of the chorda dorsalis, and probably also the 

 so-called vitreous membranes (capsule of the lens, membrana 

 Demoursii). An intercellular substance is rare in animals, for 

 the matrix of the cartilages and bones, which for the most part 

 is not excreted by the cells, but is deposited from the blood- 

 plasma or is even formed out of the cells, does not come under 

 this head. It may be said to be present in a smaller quantity 

 and more fluid, however, not only in the cellular tissues, but 

 also in the higher structures, among which there everywhere 

 exists a small quantity of connecting substance. Inter- 

 cellular spaces developed by the excretions of cells between one 

 another, have not been demonstrated with certainty in animals, 

 yet it is probable that most glandular cavities and those of the 

 heart and of the great vessels are of this nature, since they 

 appear to arise by the excretion of fluid in the interior of 

 originally compact masses of cells. 



[My view, that the genuine membrance, propria and the 

 vitreous membranes are formed as excretions, is founded par- 

 ticularly upon the examination of the chorda dorsalis and of 

 the renal canals, in which it may be readily shown that the 

 structureless membranes are secondary formations, arise in in- 

 timate union with the cells of this part, and from the very 

 first appear perfectly homogeneous. The supposition of many 

 authors, especially of Reichert, that these membranes belong 

 to the homogeneous connective tissue, is readily refuted by 

 chemical examination, since they yield no gelatine, but consist of 

 a substance which most closely approximates to the sarcolemma 

 and elastic tissue (comp. Mensonides in f Nederl. Lancet.' 

 d. iv, 694, and Donders, ibid., August, 1851, p. 73). To what 

 extent homogeneous membranes formed by excretions from 



