1906.] on The Physical Basis of Life. 401 



stage. The living cell, on this view, is like the flame in being an 

 oxygen vortex ; it is unlike it in the extraordinary latency or delay 

 in the advent of the analytic processes. 



The peculiar feature of the living cell, however, considered as a 

 machine, lies in the fact that, of the total amount of energy which it 

 acquires, a fraction is retained and devoted to the increase of its own 

 substance. In other words, it grows. After a Avhile it divides, and 

 the daughter cells are like itself, so that there is not only the power 

 of increasing the bulk of living matter by growth, but also a directive 

 faculty called heredity, which constrains the new^ living matter, made 

 from non-living matter, into the pattern of the old. The problems 

 of growth and multiplication can be reduced to their simplest terms 

 only in the case of minute forms like amoeba, each of which is at once 

 a single cell and an individual. Each individual amongst the higher 

 forms of life is built of countless cells, all of which, with one or two 

 exceptions, are predestined to death. The exceptions — the true im- 

 mortals — are chosen from the germ cells. When, however, an amoeba 

 multiplies, it divides bodily into two, and by this simple process a new 

 generation is formed. Clearly, as Weissmann first pointed out, in 

 such cases death intrudes only in the guise of accident. 



The conditions of life of these simplest forms are by no means 

 simple. Make an infusion of hay in boiling water, and let it cool. 

 In the course of a day or so it will be found to be swarming with 

 rod-like bacteria {Bacterium subtilis), engaged in feeding on the 

 organic matter dissolved out of the hay. A few days later numbers 

 of an actively mobile slipper-shaped animal, called Parammcium cau- 

 datum, make their appearance to actively swallow and digest the bac- 

 teria ; and so the round goes on. The bacteria and the paramoecia alike 

 have developed from wind-carried spores. Therefore in the natural 

 life of these creatures are periods of physiological activity alternating 

 with periods when life seems to be completely dormant — periods which 

 follow one another according to no regular sequence, but in conse- 

 quence of chance rainfall and of drought, when the inhabitants of the 

 clried-up pool are caught up and carried away as dust. 



Watch any chance collection of paramoecia, and individuals will 

 be seen not only to divide, but occasionally to fuse. Two individuals 

 swim together, adhere closely, and effect an extensive interchange of 

 substance. This is the process of conjugation : it is the first begin- 

 ning of sexual reproduction. It is followed by increased physiological 

 activity, increased rate of growth and of multiplication. If we could 

 follow this mating process fully, if our imagination could grasp the 

 events which lead up to it and the effects which follow^ we should see 

 in it the response of life to the flux of cosmical energy, just as the 

 oscillations of a particle in Brownian movement are the response to 

 the flux of electrical potential. This is no careless phrase : it is sober 

 truth, for the air currents carry and mix spores from far-distant places 

 which have had, therefore, different life-histories. Thev have lived 



Vol. XYIII. (No. lOU) ' 2 d 



