An asterisk (*) after an author's name refers to a reference in the index of 

 names. 



PART II. 

 THE BIOCOLLOIDS. 



WITH the exception of water, inorganic salts and a few organic 

 substances as, for instance, urea and sugar, only colloids exist in 

 plant and animal organisms, and if we except water, the colloids 

 quantitatively far exceed the crystalloids. This appears reasonable 

 when we consider the respective roles of crystalloids and colloids in 

 the organism. We may compare living organisms to a city, in which 

 the colloids are the houses and the crystalloids are the people who 

 traverse the streets, disappearing into and emerging from the houses, 

 or who are engaged in demolishing or erecting buildings. The colloids 

 are the stable part of the organism; the crystalloids the mobile part, 

 which penetrating everywhere may bring weal or woe. Because they 

 have only a transitory use, we find in the organism only a small 

 number and a small quantity of organic crystalloids. In plants we 

 encounter the most important organic crystalloid, sugar, on its way 

 from its place of origin to the place where it is used, or in depots, 

 such as buds, roots, fruits, etc., where it is either changed into an 

 insoluble form of carbohydrate, into starches and related products, 

 or its retreat is cut off by the drying of the stem from which the 

 fruit depends. In its course we may tap great quantities of sugar, 

 as in the birch, maple and palm when they are "in sap." If for 

 any reason it becomes mobilized again in the depots, large quantities 

 of sugar may be formed. In wild plants the amount of sugar is 

 rarely very great; it is otherwise with cultivated plants where as the 

 result of cultivation sugar is stored with no advantage to the plant, 

 e.g., sugar beets, sugar cane and common beets. At times a certain 

 biological purpose may be associated with sugar formation, e.g., the 

 sugar formation in fruits for the purpose of their dissemination. 

 The fruit is always the biological object and serves to perpetuate 

 the species, not the individual. The development of a greater 

 quantity of crystalloid as sugar in fruit is therefore not surprising, 

 since the fruit has completed its service for the individual plant. 

 Elsewhere, we find the carbohydrates only in colloidal and most 

 often even in insoluble form. I refer to starches, cellulose and gums. 



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