160 THE ENZYME THEORY OF DISEASE [CH. xi 



the power to ferment a particular sugar, if it has only recently 

 failed, is rapidly regained in the presence of that sugar. 



6. Bacterial toxins, again, are considered to be of two 

 kinds extra-cellular toxins, secreted by the bacterial cell 

 into the surrounding medium, and intra-cellular toxins elabor- 

 ated within the body of the cell and liberated only when the 

 cell itself is disintegrated. The same may be said of the 

 enzymes which ferment carbohydrates. The ferment of yeast, 

 "invertin," which transforms cane sugar into dextrose and 

 levulose, can be separated from the yeast cell. The breaking 

 up of the dextrose into alcohol and other products is a 

 property of the yeast cell itself and the ferment responsible 

 for this second stage can only be extracted when the actual 

 cell body is expressed (S. Martin, 1904). The ferments of the 

 alimentary canal may be distinguished from each other in the 

 same way. One stage in digestion is brought about in the 

 lumen of the intestine by extra-cellular ferments present in 

 the secretions. Another stage is effected within the actual 

 cells of the intestinal wall by intra-cellular ferments acting 

 upon the foodstuffs as they are absorbed. 



An emulsion of even a small portion of a glandular organ 

 may possess far more power than its actual secretion, for the 

 former contains the intra-cellular as well as the extra- cellular 

 enzymes. An emulsion of pathogenic bacteria is likewise far 

 more potent than a culture containing the same number of 

 organisms. For example, the smallest fatal dose to a bovine 

 animal of a culture of tubercle bacilli contains 20,000 million 

 organisms. The smallest fatal dose of an emulsion of the 

 bacilli contains only 5000 (Report of English Tuberculosis 

 Commission). 



7. In the seventh place, it may be observed that the 

 property of virulence is in many instances associated with 

 the power of producing fermentation. If we study two closely 

 allied organisms, one of them virulent and the other non- 

 virulent, the former will often be found to be the sugar 

 fermenter while the latter has no action in this respect. 

 For example, the Micrococcus catarrhalis is comparatively 

 non-virulent and ferments no sugars ; the gonococcus and 



