CH. XI] THE ENZYME THEORY OF DISEASE 157 



number of different diseases, and a bacteriological examination 

 of a large number of cases by Gordon showed that the disease 

 was due to infection by an organism closely resembling, if 

 not identical with, M. catarrhalis. 



Such contrasting groups of symptoms inevitably suggest 

 to our minds that something beside the mere presence of the 

 organism is responsible for them. 



4. In the fourth place, one can trace a remarkable 

 resemblance between the conditions which influence the 

 development and the loss of pathogenic power on the part of 

 micro-organisms, and the conditions which influence the 

 development and the loss of their power to ferment carbohy- 

 drates. 



(a) The addition, in small quantities, of an antiseptic — 

 such as carbolic acid — to the culture medium deprives organ- 

 isms growing in it of virulence {vide p. 75). The same agency 

 wiU destroy the power of organisms to ferment carbohydrates 

 (vide p. 55). 



(b) The influence of oxygen. Pasteur, 30 years ago, found 

 that the virulence of the organism of chicken cholera was 

 better maintained in the absence of oxygen. Anaerobic 

 growth similarly increases the virulence of the cholera spirillum 

 (Hueppe, quoted Adami, 1892). On the other hand, B. diph- 

 theriae and other organisms become less toxic if deprived 

 of oxygen. The same factor influences the activity of ferments. 

 In some cases the absence of oxygen inhibits their functions, 

 in other cases it appears to augment them. This is exemplified 

 by the sugar splitting ferments associated with bacteria. For 

 example, anaerobic growth may increase the power of the 

 dysentery bacillus to ferment maltose (Torrey, 1 905). Andrewes 

 and Horder (1906) mention a strain of streptococcus which 

 failed to ferment lactose under ordinary conditions but did 

 so readily when deprived of oxygen. 



(c) Gha/nges in temperature. It is characteristic of 

 enzymes that each one has an optimum temperature at which 

 its activities are most effective and also higher and lower 

 limits of temperature beyond which its activities altogether 

 cease. The digestive enzymes in man act most rapidly at the 



