38 GENERAL ANATOMY OF THE TISSUES. 



contents go hand in hand. Absolution is manifested in all 

 cells, but to far the greatest extent in those which at first have 

 little or no contents save the nucleus. In these, the primary 

 cause of the absorption is not to be sought in endosmose, 

 but, as Schwann has indicated, in this — that while the mem- 

 branes grow by the attraction of material from the sur- 

 rounding fluid, by virtue of their porosity they allow substances 

 to penetrate into the interior. This filling, however, does 

 not take place by the cells admitting every kind of matter 

 indiscriminately, but they exhibit peculiar relations to the 

 cytoblastema, varying with the period and with the locality; 

 so that they take up one constituent and rejeet another; and 

 the like occurs with the absorptive powers of those cells which 

 possess contents from their earliest existence. 



That this is actually the case, is demonstrated, for instance, 

 by the fact, that in embryos, notwithstanding the identity 

 of the formative material in all cells, i. e. the plasma of the 

 blood, some take up more of one substance, some more of 

 another ; and it is still more clearly evidenced by the fact, that 

 the cell-contents of probably all cells are chemically different 

 from the cvtoblastema out of which thev are formed and by 

 which they are nourished, as has been clearly shown lately, in 

 the ova and blood-corpuscles, which for example contain far 

 more potass than the blood. The reason of this phenomenon 

 may be generally stated to be, that the cell-membranes do not 

 act as mere filters, but allow one substance or another to per- 

 meate them, according to their chemical composition, the con- 

 stitution of the fluid which imbues them, their condition of 

 aggregation, and their thickness. 



Endosmose must also be taken into account as a condition 

 in the absorptive actions of cells, though hitherto it has been too 

 freely appealed to, and cells have been too often considered as 

 vesicles provided with merely indifferent porous membranes. 

 That endosmose operates is not to be denied, when it is ob- 

 served how the addition of concentrated or diluted solutions, 

 causes cells to dilate or to collapse, yet it is not easy to deter- 

 mine what influence such conditions have during life, nor what 

 results are produced by the combined operation of the ccll- 

 membranes and their contents. From a few facts in vegetable 

 physiology (growth of plants in arsenical and cupreous solu- 



