OUTLOOK. 683 



the great advantage that upon it as a foundation link after link of a tangled 

 chain of processes has been disentangled, so that as a result we have before 

 our eyes a continuous picture of separate processes. Problem after problem 

 has accumulated, and gradually a new structure has been built which 

 serves to bring under one roof all the various processes which stand in any 

 relation to the formation of the anti-bodies. The investigations of Ehrlich 

 appear especially important to us, because they are the first to bridge over 

 the chasm which has previously been assumed to exist between physio- 

 logical and pathological processes in the animal kingdom, so that to-day a 

 sharp line can no longer be drawn between these two fields. Ehrlich has 

 pointed out that the formation of the anti-bodies stands in direct relation 

 to the cell-metabolism. In order to make this relation clear, we shall explain 

 briefly how Ehrlich represents the assimilation of the nutriment by the cell 

 as taking place. The individual cells are only capable of taking up and 

 uniting with their structure those substances which correspond to their 

 entire composition. The substances taken up must fit into the cells. 

 The protoplasm possesses groups which are chemically active, and these 

 have a maximum affinity to a certain arrangement of the atoms in the 

 nutriment, which it unites to the cell-body. Paul Ehrlich calls these groups 

 side-chains, or receptors. On the basis of this theory we can easily picture 

 to ourselves why certain cells reject this and that substance, and on 

 the other hand assimilate other products. One is tempted to deduce a 

 purely chemical theory for the process of assimilation, though by doing so 

 we may be making a grave error. We can easily imagine that a chemical 

 compound, for instance the benzene ring, may carry side-chains, and that 

 these may enter into reaction with other complexes. A new compound 

 would result, but such a reaction is, as a rule, complete when this has been 

 accomplished. The cell, however, behaves in an entirely different manner. 

 It constantly utilizes material, and must be continually forming new side- 

 chains, for it is always confronted with the necessity of taking up nutrient 

 substances ; that is, the new groups must always be present to combine with 

 the nutriment. It follows from this assumption, that the "side-chains," 

 as conceived by Ehrlich, do not correspond to our present idea of a purely 

 chemical phenomenon. These side-chains are only hypothetical as yet, 

 and have nothing definite to substantiate their existence. If we assume 

 that the various cells have differently constituted side-chains, we will then 

 have reached the idea of the specific nature of the cells. This also permits 

 us to venture the assumption that the different nutrients are completely 

 disintegrated during digestion, and are transformed into homogeneous 

 products in the intestines. Ehrlich's theory is only completely compre- 

 hensible from this point of view. The specific groups of the cells must 

 exactly correspond to those of the nutrient materials, the latter being 

 established only at the time of assimilation. 



