Protoplasm. 3 5 



two sets of substances (#), secretions, and (p\ excretions, 

 which may be known therefore by the general name of 

 katastates. Both series are chemical compounds, much 

 simpler as a rule in their composition than protoplasm itself, 

 but differing from each other in one important point, viz. 

 that secretions are themselves necessary for the anabolism of 

 food matters, whilst excretions are bodies which are useless 

 and injurious to the organism, and must ultimately be got 

 rid of. Excretions include not only the products of the 

 katabolism of the protoplasm, but also of the secretions 

 after they have performed their functions. They likewise 

 include those portions of the food-material taken into the 

 organism which are useless from a nutritive point of view. 



It has been already pointed out that decomposition con- 

 sists chiefly in the oxidation of the constituent atoms of the 

 complex molecules. Further, on reference to the average 

 composition of proteids (p. 26), it will be seen that carbon 

 is by far the most important and abundant constituent. 

 Manifestly, therefore, oxidation in* the cell must mean chiefly 

 oxidation of carbon and formation of carbonic acid (CO 2 ), 

 the most abundant and most stable oxide of carbon known. 

 Katabolism must, therefore, be accompanied by a plentiful 

 production of carbonic acid, the process of excretion of 

 which is known by the special term of respiration. 



In addition to these changes, there are others which result 

 in the separation of part of the protoplasm to form a young 

 cell or cells. Vegetative multiplication and reproduction 

 are the terms applied to such changes ; the discussion of 

 both is, however, postponed for the present. 



SECTION III. PHENOMENA. CONCOMITANT WITH MANI- 

 FESTATIONS OF ENERGY BY LIVING PROTOPLASM. 



Having considered the various manifestations of energy 

 in living protoplasm viz. contractility, irritability and au- 

 tomatism, reception and assimilation of food, metabolism, 



