286 IV. THE PRINCIPLES OF LIFE PHENOMENA 



As aleady stated, the primary organisms might have been generated 

 and evolved by affecting other organisms or protoplasm-like polymerized 

 proteins in rearranging their structure just as viruses multiply in the 

 host cell. However, when such primitive primary organisms or the 

 masses of assimilase evolved to a certalli extent, they might have to 

 rearrange the structure of free protein molecules or to synthesize pro- 

 tein molecules from smaller components to incorporate them into their 

 bodies. If they evolved up to such a stage and were capable of syn- 

 thesizing proteins, considerable quantities of energy would be neces- 

 sary for the active and incessant structural change of protoplasm pro- 

 tein as well as for this function, and the energy required would be 

 supplied by the decomposition of high molecular substances which 

 might have been either synthesized by utilizing the energy of the sun 

 or taken from other organisms. 



Life may be nothing but the manifestation of the function of 

 assimilase. If an assimilase was once generated and had to continue 

 its existence, as a necessary consequence it would evolve and become 

 to have complicated structure until the form and the function of 

 undoubted organisms were obtained. It would be unable to become 

 more fitted unless it was advancing continuously. Thus, assimilase 

 might have to choose between the extinction and the advancement, 

 and if the advancement reached to a certain extent the development 

 of metabolic system would follow as a natural consequence. 



In both cases of the primary and the secondary organisms, be- 

 fore they had enough evolved to synthesize proteins from smaller 

 components, they might have to acquire the faculty to rearrange the 

 pattern of free protein molecules, the structure of which was only 

 slightly different from those of the organisms, in order to incorporate 

 the molecules into them. It is well known that primitive secondary 

 organisms, such as the organism of bovine pleuropneumonia, can 

 sometimes multiply outside the host if blood-plasm proteins are added 

 to the medium. Such organisms may be looked upon as having ac- 

 quired this faculty. In addition, it seems possible that the cells of 

 higher animals existing at present still adopt this easy way of as- 

 similation. Thus it has been claimed that dogs can be kept in health 

 when the only source of nitrogen is blood-plasm injected in their 

 veins (108). The animal must, therefore, be able to form any required 

 protein from the protein present in the plasm without preliminary 

 hydrolysis by the enzymes of the digestive tract. Only a little energy, 

 if any, may be required for such an easy assimilation procedure, in 

 which are utilized complete protein molecules that have the structure 

 not greatly different from that of the protein composing the assimilase 

 itself. 



