14 INTRODUCTION 



introduced by the food or growing in the digestive 

 tract, and secreting special enzymes. 



In the vegetable kingdom, the chlorophyll acts 

 as an enzyme in the production of carbohydrates 

 from carbonic acid and water. But chlorophyll 

 occurs in such large quantities that it has been 

 possible to subject it to ordinary chemical analysis 

 (cf. the work of Willstatter and others), and there- 

 fore it does not belong to the substances with which 

 we deal in this book. But the vegetable kingdom 

 produces and uses ferments or enzymes of the same 

 action as those known from the animal kingdom. 

 Well known are the very active lipase contained in 

 castor beans, the proteolytic ferment papayotin from 

 Carica Papaya, and another proteolytic ferment in 

 growing seedlings of barley. Further, we know a 

 great number of katalases, oxydases, and reductases 

 both from the animal and from the vegetable 

 kingdom. Of high importance are the enzymes 

 furnished by the yeast-cells, namely, zymase, which 

 causes alcoholic fermentation ; invertase, which de- 

 composes cane - sugar ; and maltase, which splits up 

 maltose. 



In general, micro-organisms produce a large 

 number of substances of high chemical activity. 

 Amongst these a great many are of the highest 

 interest for us, as, for instance, the diphtheria toxin or 

 the tetanus -poison, which cause the terrible diseases 

 diphtheria and lock-jaw. Even higher organisms, 

 as snakes or spiders or insects, produce similar 

 poisons, as do also some plants, e.g. Abrus praeca- 



