i 5 6 AGE, GROWTH, AND DEATH 



advancing organisation and of advancing age. It is 

 certainly somewhat paradoxical to assert that the in- 

 crease of the protoplasm is a sign of old age, a sign of 

 senescence, since protoplasm is the physical basis of 

 life. It undoubtedly is such, and we should hardly 

 anticipate that its increase would have a deleterious 

 effect. But such is, it seems to me, clearly the case. 

 But it is not merely, of course, a question of the in- 

 crease of protoplasm which we must bear in mind in 

 estimating the cause and effect, but also the question 

 of differentiation, in consequence of which protoplasm 

 becomes something else and different from what it 

 was before. This alteration, then, together with the 

 increase of the protoplasm, is the change which in all 

 parts of the body marks the passage from youth to 

 old age. 



It seems to me not going at all too far to say that 

 the increase of protoplasm is a fundamental pheno- 

 menon. I wish to give you a more precise notion of 

 this increase ; and I am glad to be able to do so in 

 consequence of a research carried on by Professor 

 Eycleshymer in my laboratory and completed by him 

 afterwards in his own laboratory at the University of 

 St. Louis. 1 He studied the development of the muscle 

 fibres in the great salamander, known scientifically by 

 the name of Necturus. These muscle fibres are some- 

 what cylindrical in shape. Their ends can be accurately 



1 A. C. Eycleshymer, "The Cytoplasmic and Nuclear Changes in the Striated 

 Muscle Cell of Necturus" American Journal of Anatomy, iti., 285-310. This 

 paper is of exceptional importance as a contribution to our knowledge of the life- 

 history of cells. 



