104 BACTEKTOLOaTCAT. CHEMISTRY 



is incubated with a .sulutiuii of the compound to be 

 examined and a standard quantity of methylene blue 

 solution, all buffered at an appropriate 2>H value in an 

 evacuated system. If the bacterium is capable of acti- 

 vating the substrate as a donator of hydrogen (that is, 

 if it is capable of oxidising it) the methylene blue accepts 

 the hydrogen and becomes reduced to the colourless 

 leuco -compound, the loss of colour serving as an indicator 

 that the reaction has occurred. By this means numerous 

 fatty acids, hydroxy- and amino-acids, polyhydric alcohols 

 and sugars have been shown to be activated as hydrogen 

 donators. Some of these substrates are much more 

 readily activated than others, the most active, glucose, 

 being some ten thousand times more effective than the 

 least active of the lower fatty acids. Formic, lactic and 

 succinic acids are all fairly active. All bacteria do not 

 activate the same compounds, and there are marked 

 differences between the activation by plant and animal 

 tissues and by bacteria. 



Thunberg, who originated the methylene blue 

 technique, considered these activations as being due to a 

 series of specific enzymes. This is rather hard to believe, 

 however, since Esch. coli, for instance, would need to 

 contain over fifty such enzymes, including some for sub- 

 stances like chlorates which the organism would be 

 extremely unlikely to meet in the ordinary course of its 

 existence. Quastel has suggested that one general 

 mechanism is responsible for all these activations, which, 

 after all, are alike in that they are all hydrogen transfers. 

 He considers that the enzyme action depends on two 

 factors ; first that the substrate is adsorbed on an active 

 surface in the cell, and secondly that the adsorbed mole- 

 cule is rendered unstable in such a way that it is liable 

 to lose hydrogen if it is a donator or to gain hydrogen 

 if it is an acceptor (like methylene blue). The cell is 

 pictured as having a network of internal interfaces, 

 probably composed of protein and lipoid constituents. 



