OUTLOOK. 667 



dependent upon that of the cell proteins. Thus their activity is regulated 

 very delicately, and the foundation is laid for a specific cell-metabolism. 

 The original structure of the cell determines its characterization for the 

 whole of its existence. Although we do not doubt that the various tissues 

 possess, corresponding to their functions, variously constituted cells, the 

 differences of which are apparent not only in the metabolic end-products, 

 but especially in the nature of the secreted substances, we can, on the 

 other hand, imagine that all the cells of one and the same nature have com- 

 mon outlines along certain lines, so that a common character marks the 

 whole cell structure of an individual. 



Now an individual results from the union of two cells, the egg and sperm- 

 cells of the same nature. Each must contain within itself the common 

 form of cell composition, and thereby possess the kind of cell-metabolism 

 which is characteristic of this particular species. All the cells which result 

 in rapid succession from the fertilized egg-cell can only assume these char- 

 acteristic tendencies, and thus the chemical unity of the original cell guar- 

 antees the maintenance of the species. This is subsequently maintained 

 by the activity of the intestine, which only permits such material to reach 

 the tissues as has been previously prepared in a definite manner for the 

 entrance into cell-metabolism and into the cells themselves. We do not 

 mean to assert that the body cells have lost the ability themselves to trans- 

 form and adjust to their composition and to their metabolism any foreign 

 nutriment, or especially any foreign protein. The unicellular organisms 

 must be able to cause all these processes to take place side by side. With 

 the higher animals, the function of transforming the foodstuffs is relegated 

 almost exclusively to the intestine. There is here a division of labor. 1 

 We can easily imagine that by reason of an imperfect function of the intes- 

 tine, an insufficient amount of prepared material may be carried to the 

 tissues, and that under some circumstances the entire chemism of the 

 cells, their structure and at the same time their metabolism, may become 

 altered so that finally degenerations result which are apparently 

 inexplicable. 



In mammals the individuality of the cells of the species is in a very great 

 measure guaranteed by the longer or shorter period during which the new 

 being remains associated with the organism of the mother. The foetus 

 obtains its nourishment from the blood of the maternal organism; the 

 suckling from her milk. 



We have thus arrived at a purely chemical explanation for the concep- 

 tion of species and its maintenance. We admit that we are reasoning 

 from a limited number of observations, and are not yet in a position to 

 demonstrate experimentally the truth of our conception. We realize fully 



1 Cf. Ulrich Friedemann and S. Isaac: Z. exper. Path. u. Therapie, 1, 513 (1904). 



