8 



METABOLISM 



a sample of protoplasm as could be obtained (such as that carried out by 

 REINKE and RODEWALD, 1881-3), was therefore of the greatest value. These 

 investigators selected for the purpose the plasmodium of one of the Myxomy- 

 cetes, viz. a mass of naked protoplasm, unenclosed by a cell-wall. Three quarters 

 of this plasmodium was found to consist of water. The substance, when air- 

 dried, gave on analysis about 5 per cent, of water and 28 per cent, of calcium 

 carbonate. Since neither of these bodies can be considered as the specific 

 medium of vital manifestations we may neglect them altogether. In addition, 

 the air-dried plasmodium contained a large number of chemical compounds 

 which could be estimated only approximately, and which did not lend them- 

 selves to accurate analytical determination. These estimates are summarized 

 in the following table (REINKE, 1901. 232) : 



1. Proteids containing phosphorus (plastin and nuclein) about 



2. Proteids not containing phosphorus 



3. Amide bodies . 



4. Fats . 



5. Lecithin 



6. Cholesterin 



7. Carbohydrates . 



8. Resin 



9. Salts of organic and inorganic acids 

 10. Undetermined or not specified bodies 



40-0% 



12-0% 



o-3% 



2-0% 

 12-0% 



'5% 



100-0% 



We have already drawn attention to the fact that a series of metabolic 

 processes takes place in the plant, consisting in the absorption of materials 

 from the environment, the alteration of these in the plant, and an excretion of 

 certain substances which have become of no further use ; to this we must 

 now add a further statement, viz. that these metabolic processes are primarily 

 associated with the protoplasm. Chemical analysis of the protoplasm of the 

 Myxomycetes does not give us any indication which of the compounds so 

 determined form part of the special living protoplasm and which are to be con- 

 sidered as products of metabolism. REINKE expressly states that the plas- 

 modia which he investigated were in the act of forming fructifications, and 

 therefore were not likely to contain any unaltered nutritive materials ab- 

 sorbed from the environment. Since, however, the proteid, fat, and carbo- 

 hydrate, known to occur in large quantities in the seeds of the higher plants, 

 cannot be considered as genuine protoplasm, but rather as dead material 

 deposited in these situations as plasta for the construction of the seedling, 

 we are bound to regard the greater part, it may be, of the materials determined 

 by REINKE as belonging to the category of so-called reserve materials. Again, 

 it would be quite an arbitrary proceeding to designate any of the substances 

 mentioned in the table quoted above (such as, e.g., the dominant proteids which 

 contain phosphorus) as the essential, still less as the only constituents of 

 protoplasm itself. It is possible that protoplasm, the true living substance, 

 consists essentially of a mixture of many materials ; there can, however, be 

 only one substance with vital characteristics, and there is considerable 

 evidence forthcoming, as we shall discover later on, tending to show that it 

 is not unlikely that this substance exists only in relatively small quantity. 



A further problem now confronts us. Is life bound up with one definite 

 substance, which we may term ' the life-bearer ', or does life arise from some 

 special arrangement of lifeless bodies ? It has often been the habit to liken the 

 organism to a machine, and analogies between them are not wanting. But 

 the work of a machine depends, in the first instance, not on the chemical nature 

 of the substance of which its parts are composed, but on their mode of con- 

 struction and on their arrangement. Whether we make a machine of brass 



