SOME CURRENT THEORIES 437 



the result of the multicellular condition with its accompanying 

 differentiation. In such organisms the struggle for existence among 

 the parts which Roux ('81) believed to be of such fundamental 

 importance in organic life must lead finally to the death of the 

 whole. 



The change in the relation between surface and volume in the 

 cell and the organism during growth has often served as the founda- 

 tion for speculations concerning growth and its cessation, aging and 

 death, and cell division. Since the volume of the cell or the 

 organism increases more rapidly than its surface, and since nutrition 

 and oxygen enter through the surface, it is argued that as the cell 

 or the organism increases in size the amount of nutrition and oxy- 

 gen which can enter through the surface must become less and less 

 adequate for the needs of the growing cell mass. Sooner or later 

 a stage may be reached where only the superficial parts of the cell 

 receive sufficient nutrition, and finally the death of the cell may 

 result from the starvation of the parts farthest from the surface. 

 Various authors, among them Herbert Spencer, Bergmann and 

 Leuckart, and later Verworn, have called attention to the biological 

 importance of this relation between surface and volume and have 

 employed it as a basis for theoretical considerations concerning 

 one aspect or another of life. Recently Muhlmann ('oo, '10, '14) 

 has advanced a theory of senescence and death based upon this 

 p rinciple. According to Muhlmann growth brings about senescence 

 and death because it leads sooner or later to starvation of the parts 

 of the cell or the organism farthest from the surface. In the uni- 

 cellular forms the nucleus reacts to the extreme stage of starvation 

 by division, which is followed by cell division, and so an increase 

 of nutritive surface is produced; but in multicellular organisms, 

 where the cells do not separate from each other, cell division only 

 leads to further growth and so to starvation, which is most extreme 

 iii the part farthest from the surface. Old age is then a condition 

 of starvation which according to Muhlmann is most extreme in the 

 central nervous system, the part farthest removed from the nutri- 

 tive surfaces, and death is consequently primarily a death of the 

 nervous system. Death for Muhlmann is not only the cessation 

 of life, as it occurs in man and the higher animals, but the division 



