CHEMICAL BASIS OF THE ANIMAL BODY. 73 



brevity. We shall perhaps be not far wrong in considering that as 

 regards the organised ferments the changes they effect may be, in their 

 earlier stages, partly the outcome of the action of some soluble 

 enzyme and partly the result of that cycle of metabolic (chemical) 

 processes which occur continuously in their protoplasm, in virtue of 

 which they are spoken of as 'living.' Similarly in the higher 

 animals we find a large number of simpler processes carried on by 

 means of isolable enzymes, by which undoubtedly the labours of the 

 protoplasm in performing its own more complicated activities is 

 materially lightened. But we are still face to face with numberless 

 decompositions which cannot as yet be reproduced outside the 

 limits of living matter and which cannot be explained with reference 

 to anything other than the direct activity of living matter. 



The general conditions and factors which characterise the action of 

 the soluble ferments or enzymes have already been mentioned (p. 53) but 

 without making any suggestion as to the probable way in which they 

 produce and carry on the decompositions to which they give rise. 

 Liebig's theory of the mode of action of yeast, since it left the organi- 

 sation and life of the cell entirely out of account, and was based simply 

 upon the supposed properties of the changing cell-substance, might ob- 

 viously therefore be applied to any ordinary soluble enzyme. There is 

 however no evidence to show that the enzymes are in the state of change 

 or decomposition which Liebig supposed ; on the contrary they are ob- 

 served to be on the whole remarkably stable substances, from the point 

 of view that a minute trace can produce a profound decomposition in a 

 relatively enormous mass of material, during an almost indefinitely long 

 time, without itself undergoing any proportionate alteration or destruc- 

 tion 1 . The theory of v. Nageli previously quoted was applied by its 

 author to explain the fermentative power of the living cell and is thus 

 not directly applicable to the non-living enzymes. Mayer it is true has 

 put forward a view which is essentially a development of v. Nageli's 

 and is applicable to the enzymes. These substances are in all cases 

 produced solely and entirely by the activity of living cells or organisms, 

 and Mayer regards them as retaining in themselves a portion of that 

 molecular motion which is supposedly so characteristic of the living 

 parent cell from which they have been separated 2 . It cannot however 

 be said that these theories afford any real insight into the probable 



1 Berzelius explained. fermentation as the outcome of a mysterious 'catalytic 

 action,' or ' action by presence ' or ' contact.' He thus compared ferments to platinum- 

 black, which is able, in minute quantity, to cause a liberation of oxygen from peroxide 

 of hydrogen without itself undergoing any recognisable change. This is however no 

 explanation, for it does not amount to more than saying that given the contact of 

 two substances capable of reacting on each other, a certain reaction takes place. 



2 Die Lehre von den chem. Fermenten, Heidelb. 1882. 



