lOOO.] 0)1 The Physical Basi.^ of Life. 403 



Calkin. Therefore, when the period of decay had arrived and the 

 individuals were dying off rapidly, he tried placing them in various 

 infusions. Vegetable infusions were without effect, but infusions of 

 animal tissues, and particularly beef extract, gave the required result. 

 The rate of growth and of reproduction reached the normal level, and 

 death ceased. Senile decay had given way to artificial rejuvenation. 

 Instead of 170 generations being the limit, by stimulations in the 

 periods of depression Calkin succeeded in carrying a race to the 740th 

 generation, and Woodworth to the 860th generation, when tlie indi- 

 viduals were still healthy and fully active. The living matter of these 

 cells without doubt is potentially immortal ! 



Consider for a moment what incredible chemical activity and 

 stability of character these figures imply. If it was possible to pre- 

 serve alive all the individuals, then at the 900th generation we should 

 have a number which would need a row of some hundreds of figures 

 to express. The parent cell would have produced the 900th power 

 of two individuals like itself. The increase in the bulk of active living 

 matter which would have been formed from non-living had there 

 been space enough and food enough is not less wonderful. At the 

 350th generation it would have the dimensions of a sphere larger than 

 the known universe !* And the surface of the sphere would be 

 growing outwards at the rate of miles a second. Nor is this all, for, 

 in addition to the enormous chemical activity implied by a rate of 

 growth wliich would, if unchecked, produce a mass of living matter 

 larger than the known universe in less than two years, there has been 

 thimighout continuous expenditure of energy on incessant and active 

 movement. These animals have been watched continuously for five 

 days, and throughout that time they were ceaselessly moving ! 



" The recurring periods of depression show that in the living 

 machine repair is not complete, and that after a time it will, if left 

 to itself, cease working. With the condition of ill-repair there is 

 associated a feature of singular intei-est. Woodworth specially draws 

 attention to the fact that in the periods of depressed vitality the 

 transmission of characters is imperfect. The moulding power of 

 heredity fails, and many " monsters " are born. 



Rejuvenescence can be brought about by a great variety of media, 

 by extracts of muscle, of brain, of pancreas, by simple salts, by 

 alcohol even. It is not food, but a marked and abrupt change of 

 state that is needed— a stimulant, in fact— and beef extract produces 

 its effect not qid food, but as a stimulant pure and simple. Senile 

 decay is due to monotony, under the influence of which the vital 

 potential wears out ! 



The action of alcohol is remarkable. It was added to the water 

 in which the animals lived so that they were always immersed in a 



* I owe this rough calculation to my friend Mr. Punnett. 



2 D 2 



