22 METABOLIC PHENOMENA. [sect. 1 3. 



to time and place, quite definite relations to the cytoblastema, 

 rejecting one constituent of it and taking up another; and the 

 same thing occurs with the absorptive power of those cells which 

 possess contents from the first moment of their formation. That 

 this is really the case, is, for example, proved by the circum- 

 stance, that in embryos, notwithstanding the uniform formative 

 material, i.e. the blood-plasma, for all the cells, some take up more 

 of these, others more of those materials, and from this results still 

 more distinctly that the contents of probably all cells are chemically 

 different from the cytoblastema by which they are formed and main- 

 tained, as has recently been more clearly demonstrated in ova and 

 blood-corpuscles, the latter, for example, containing much more 

 potass than the blood. The reason of this phenomenon may be 

 thus stated in general terms, that the cell-membranes do not act 

 like simple filters, but allow one substance or another to permeate 

 them, according to their chemical composition, the nature of the 

 surrounding fluid, their condition of aggregation, and their thick- 

 ness. True endosmosis, which has frequently been assumed as 

 occurring in the cells, does not, according to my observations, 

 appear to occur, in as much as the cells in their totality rather 

 present the condition of simple bodies saturated with fluid. 



The substances composing and taken up by the cells, undergo 

 manifold metamorphoses, in consequence of the vital process. 

 These metabolic phenomena {Schwann) are referable, firstly to the 

 cell-membrane, and secondly, to the cell-contents. With regard to 

 the former, this much is certain, that the membranes of most cells 

 not only become thicker and firmer with age, but also assume 

 other chemical properties; yet it is impossible in the individual 

 case to say to what the change is due. In the horny structures, 

 the membranes of the young cells are readily soluble in alkalies 

 and acid, whilst subsequently they resist it in part very much- 

 the same thing is found in the higher elementary parts, as the 

 nerve-tubes, animal muscular fibres, and the capillaries, in which 

 the sarcolemma, the sheath of the nerve-tubes, and the capillary 

 membrane, which have the signification of metamorphosised cell- 

 membranes, re-act quite differently from the primitive formative 

 cells. In the cartilage-cells also the membranes become more re- 

 sisted with age, and the same occurs with the cell-membranes of 

 the ova of many animals, as is best shown in fishes. These 

 examples, which might be multiplied, may suffice to establish 

 the occurrence of metamorphoses of the cell-membranes; sub- 

 sequent investigation will have to show upon what these de- 



