86 MICROBES AND TOXINS 



they have remained at that stage : they have not cast off the 

 necessity for ready-formed organic food, i.e., the parasitic habit, 

 nor can they break up the carbonic acid of the air, liberating 

 oxygen and absorbing carbon. The purple bacteria then occupy 

 a position intermediate between the saprophytic or parasitic 

 habit of bacteria in general and the chlorophyll property of the 

 higher plants. They carry on, like the latter, a sort of photosyn- 

 thesis, but what they synthesize with the aid of light is still 

 organic material like the ordinary bacteria. 



Secretion of Diastases or Enzymes. Microbes act 

 through their diastases ; fermentations are thus diastasic 

 reactions. The diastases carry on the transformations of 

 matter both by breaking down and building up, and it is 

 through them that the bacteria transform energy. 



The discovery of diastases and the possibility of extracting 

 them, of isolating them (not completely pure), and of making 

 them act without the presence of living cells, represents a great 

 acquisition to the dominion of chemistry in the field of the 

 study of life and fermentation. 



A further step was made when Bertrand demonstrated the 

 prominent role taken by the mineral elements associated with 

 the enzymes ; the activity of laccase depends on the proportion 

 of manganese present, and the whole reaction behaves as if 

 laccase were a salt of manganese with a weak acid. Besides, 

 all the diastasic reactions can be performed by chemical agents 

 and the part played by diastases seems to be that of amplifying 

 and stopping the action of the latter. 



The nature of diastases is still unknown, and we shall not 

 dwell here upon the manner of preparing them, on the causes 

 of error which may creep into this technique, or on the theory 

 of diastasic actions in general. 



One microbe is capable of secreting several diastases. 

 With the proteolytic enzymes have been grouped the lysins 

 including the haemolysins of bacteria. The solution of the 

 cell attacked may indeed be only the sequel to an action on 

 the cell membrane or protoplasm, injurious but not actually 

 dissolving. The best known haemolysins are those of the 



