LECTURE IV. 

 CARBOHYDRATES. 



III. 

 METABOLISM OF CARBOHYDRATES IN PLANT AND ANIMAL ORGANISMS. 



FORMERLY the biology of plants occupied a sharply distinct field from 

 that of the animal organism. The two kingdoms were believed to be 

 opposed to one another with regard to the transformations of energy and 

 of force taking place within each. Plants were alone held to be capable of 

 building up organic substances, i.e., to be capable of effecting syntheses. 

 The animal system, on the other hand, served to break down such sub- 

 stances. In this way the animal and vegetable worlds acted in conjunction 

 and formed a large unit. However, the more scientists penetrated into 

 the intricacies of vegetable and animal metabolism, and in proportion to 

 the comparative studies made, the more it became evident that there was 

 no sharp line to be drawn between these two fields. When Wohler in 1824 

 discovered that benzoic acid introduced into the animal body was not 

 consumed nor eliminated as such, but was to be found in the urine com- 

 bined with glycocoll in the form of hippuric acid, the path was broken, 

 and for the first time a synthetical process was recognized as taking place 

 in the animal organism. 



In the following period, as we shall see, a large number of such syntheses 

 were discovered as taking place in the organism of animals, and to-day 

 there is no longer any doubt but that synthetical processes play an 

 important part therein. To be sure, in importance, and, as far as we know, 

 in variety also, they are far in the background as compared to the syntheses 

 in plant organisms. On the other hand, plants utilize oxygen and produce 

 carbon dioxide from more complicated compounds; in other words, they 

 break down substances. In this way physiology has given a new and pow- 

 erful support to the well-known common morphological outlines of the two 

 kingdoms, so that to some extent the two fields have been placed upon a 

 common basis although each retains a* certain degree of independence. 



Nothing supported the old conception of the sharp distinction between 

 the synthetical processes of plants on the one hand, and the catabolic pro- 

 cesses taking place in animal organisms on the other hand more than the 



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