STUDIES IN THK RETINA. 357 



fibrils is a known phenomenon in the process of nerve 

 regeneration. Thus, in almost every pointy the ground has 

 been trodden by previous workers. Most of their observa- 

 tions have, however, remained isolated and fragmentary. 

 The foregoing study of the retina has enabled us to link them 

 all together. 



There remains, however, a whole field of facts and theories 

 relating to protoplasmic structure based largely upon obser- 

 vations of an entirely different character. All our observations 

 are purely microscopic, and it may be of interest for a moment 

 to compare the results with those obtained by chemistry or by 

 experimental physiology. Professor Verworn has recently 

 attempted to co-ordinate them by means of the biogen hypo- 

 thesis.i According to this, there are certain very complicated 

 molecules, the " biogens," whose activities in presence of 

 certain other substances, oxygen on the one hand and nutri- 

 tive carbohydrates on the other, may be made to account 

 for most of the known phenomena of metabolism. These 

 molecules are said to have their chief seat in the cytoplasm 

 and not in the nucleus, which is, in essence, a reserve depot 

 for the oxygen and other chemicals necessary to enable the 

 biogens to perform what is required of them for the vital 

 processes with the carbohydrates derived from food. The 

 real test of this theory as a working hypothesis must 

 naturally come from physiological chemistry, but morphology 

 cannot be left altogether out of account. One of the chief 

 problems of the biogen hypothesis is how to picture the 

 several factors distributed in space within the cell so that 

 they may always be in contact with or within reach of one 

 another for their mutual reactions. It seems to me that 

 the description above given of the fundamental structure 

 of protoplasm may possibly supply an answer. If the proto- 

 mitomic filaments are strands or chains of biogens, then we 

 have these latter, with a specially dense and usually more 

 passive part of their reticulum, immersed in the reserve depot 

 of the chemicals necessary for their activity (the nucleus). 

 ' Max Verworn, ' Die Hioj^cii-lIvpotJicso,' Jcn;i, l!*02. 



