146 THE CELL 



very varying chemical composition, and muscle and nerve fibres, 

 which, in consequence of their peculiar organisation, are endowed 

 in a special manner with contractility and the power of conduct- 

 ing stimuli. In the last case the chemical activity of the cell 

 assumes a character which Max Schultze has designated as its 

 formative activity. The protoplasm makes use of the raw ma- 

 terial which is brought to it, and prepares from it often very 

 wonderfully constructed substances, which answer special pur- 

 poses. In this activity the cell appears, to a certain extent, like a 

 builder, or, as Haeckel (V. 4b) has it, like a modeller or sculptor. 



This formative activity of the cell, or, as it is better expressed, 

 the power of the protoplasmic body to create different structures, 

 is of extreme importance; for it is solely due to this power that 

 there is so great a diversity of elementary particles, in consequence 

 of which the animal body is able to attain to so high a degree of 

 pei-fection. The division of labour, which is so successful amongst 

 cells, is based solely upon this foundation, and by its means the 

 capacity for work of the cell community is rendered much greater. 



Hence this subject of the assimilation of material must be 

 examined from two points of view ; the first is a chemical one, in 

 so far as it treats of the formation of innumerable substances by 

 means of the protoplasm, whilst the second is more morphological, 

 in so far as the various substances present in the protoplasm may 

 be seen to differ from it, to occupy a definite position, to have a 

 fixed form and structure, and to obey special laws of development. 



One of the most important tasks for the biological chemist of 

 the future is to render accessible to morphological investigation 

 the various substances distributed throughout the cell body by 

 means of differential staining mixtures. 



1. Chemistry of Assimilation. The chemical processes of the 

 cell, which are at present shrouded in mystery, can only be 

 treated here in so far as they are connected with fundamental 

 problems, such as the synthesis of carbo-hydrates, fats, and pro- 

 teids out of more simple elementary substances. 



The chemical processes in the animal kingdom appear to differ 

 considerably from those occurring in the vegetable kingdom. 

 Only that protoplasm present in plant cells, which contains chloro- 

 phyll, is able to make high molecular ternary compounds out of 

 carbon dioxide and water ; the protoplasm which does not contain 

 chlorophyll, and which is present in animals and certain colourless 

 portions of plants, is only able to undertake further synthesis 



