86 BIOLOGY: GENERAL AND MEDICAL 



hence we find at the bottom of the scale of living things, 

 forms that are able to seize upon relatively simple in- 

 organic compounds combining them into more and more 

 complex compounds and integrating them into living 

 protoplasm, while at the top of the scale of life we find 

 organisms whose appearance must have come relatively 

 late in time, that are unable to make use of any of the 

 simple inorganic substances, and are absolutely depend- 

 ent upon the lower antecedent forms for food. 



How the animal substance reintegrates itself and 

 builds up additional animal substance by appropriating 

 to its uses the equally complex substance of other 

 individuals or the slightly less complex products of their 

 disintegration, it is beyond the knowledge of chemists 

 to give any adequate information, for we neither know 

 the nature of the substance being integrated nor that of 

 the substances by which it is being integrated. 



On the other hand, when we inquire how the more 

 simple vegetable organisms are nourished, the problem 

 is simplified, for, though the vegetable protoplasm is 

 still too complex for us to follow in its transformations, 

 the compounds with which and upon which it works are 

 so simple and so well-known that we can easily follow 

 them through many transformations. In doing this, 

 however, we find the living substance capable of perform- 

 ing miracles of chemical synthesis, the experimental 

 reproduction of which is impossible. 



Of the numerous elements that are said to enter into 

 the composition of living substance many have been 

 mentioned that find no place in the hypothetical struc- 

 ture of the proteid molecule. It is by no means certain 

 that these elements find a place in the composition 

 of protoplasm. They are discovered by an examina- 

 tion of masses of tissue composed of protoplasm and its 

 numerous products, not by examination of the elemen- 

 tary substance itself. A single elementary mass of pro- 

 toplasm a cell is so small and the quantity of these 

 elements so minute that they must inevitably elude 



