CHAPTER XI 



THti ENZYME THEORY OP DISEASE 



IT is impossible to leave this subject without some further 

 mention of a theory, to which passing reference has already 

 been made more than once in the foregoing pages, namely the 

 Enzyme theory of disease. 



This theory predicates that the results which follow, and are 

 regarded as characteristic of, infection by a certain organism 

 including both the pathological lesions produced and the 

 train of symptoms observed clinically are caused not only 

 (if at all) by the activities of the micro-organism itself, but 

 by the activities of ultra microscopic bodies of the nature of 

 enzymes which are associated in each case with a particular 

 bacterial cell in the same way that the ferments of yeast are 

 associated with a particular vegetable cell. 



If the scattered references to this theory in the foregoing 

 pages be collected together they will be found to constitute 

 a by no means negligible weight of evidence in favour of it. 

 The considerations which lend support to the theory are the 

 following. 



1. In the first place, there is the observation that a sapro- 

 phy tic organism incapable at one time of giving rise to disease, 

 even after it has invaded the living tissues, may suddenly ac- 

 quire pathogenic powers and give rise in the living body to 

 definite lesions and a definite group of symptoms. Harmless 

 organisms such as the saprophytic pneumococcus, the Micro- 

 coccus catarrhalis and B. coli, for example, may mysteriously 

 acquire the power to produce respectively pneumonia, menin- 

 gitis and enteric fever. On the other hand, virulent pathogenic 

 organisms such as the Klebs-Loeffler bacillus, the meningo- 

 coccus and B. typhosus may as mysteriously become deprived 

 of their power to produce respectively diphtheria, meningitis 



