152 THE CELL 



This is especially true of all the processes which are described 

 above as belonging to the formative activity of the cell. What 

 relationship does the protoplasm bear to its organised products, 

 such as the cell membrane, the intercellular substance, etc.? 



Two quite opposite views have been suggested upon this sub- 

 ject. According to the one, the organised substances are formed 

 by the transformation of the protoplasm itself, that is to say, 

 through the chemical rearrangement or splitting up of the proto- 

 plasmic molecules ; according to the other, on the contrary, they 

 are supposed to be formed of plastic materials, carbo-hydrates, 

 fats, peptonised proteids, etc., which are taken up during meta- 

 bolism by the protoplasm, conveyed to the place where they are 

 required, and there brought into a suitable condition for secre- 

 tion. 



This difference may be best explained by an example, such as 

 the formation of the cellulose membrane of the plant cell. 



According to a hypothesis which has been strongly supported by 

 Strasburger (V. 31-33) amongst others, the microsome containing 

 protoplasm becomes directly transformed into cellulose lamella ; 

 that is to say, cellulose, as a firm organised substance, is formed 

 directly out of the protoplasm. 



Another theory is, that some non-nitrogenous plastic substance, 

 such as glucose, dextrin, or some other soluble carbo-hydrate, forms 

 the materials from which the cell membrane is constructed. 

 These materials are conveyed by the protoplasm to the place 

 where they are required, and are here converted into an insoluble 

 modification, cellulose. Since this cellulose acquires a fixed struc- 

 ture from the beginning, the protoplasm must, in a manner at 

 present unknown to us, assist in its construction ; this process is 

 described by the expression " formative activity." 



According to the first hypothesis, the cellulose membrane may 

 be described shortly as a metabolic product of the protoplasm, 

 and, according to the second, as a separation product of it. 



The question of the formation of chitinous skin, of the ground 

 substance of cartilage and bone, of calcareous and gelatinous sub- 

 stances, may also be regarded from the same two points of view ; 

 in fact, all conceptions of the metabolism of the cell present the 

 same difficulty. 



Claude Bernard (IV. l a ) described this relationship in the 

 following words : " From a physiological standpoint it may be 

 Conceived that in the organism only one synthesis occurs, that of 



