THE DURATION OP LIFE. 33 



upon the degree of fertility, but not upon the duration of life. 

 Climatic considerations, especially the periodical changes of summer 

 and winter, or wet and dry seasons, are here of greater importance. 



It must then be admitted that the dependence of the duration of 

 life upon the external conditions of existence is alike common to 

 plants and animals. In both kingdoms the high multicellular 

 forms with well-differentiated organs contain the germs of death, 

 while the low unicellular organisms are potentially immortal. 

 Furthermore, an undying succession of reproductive cells is possessed 

 by all the higher forms, although this may be but poor consolation to 

 the conscious individual which perishes. Johannes Muller is there- 

 fore right, when in the sentence quoted at the beginning of my 

 lecture, he speaks of an ' appearance of immortality ' which passes 

 from each individual into that which succeeds it. That which 

 remains over, that which persists, is not the individual itself, 

 not the complex aggregate of cells which is conscious of itself, 

 but an individuality which is outside its consciousness, and of a low 

 order, an individuality which is made up of a single cell, which 

 arises from the conscious individual. I might here conclude, but 

 I wish first, in a few words, to protect myself against a possible 

 misunderstanding. 



I have repeatedly spoken of immortality, first of the unicellular 

 organism, and secondly of the reproductive cell. By this word 

 I have merely intended to imply a duration of time which appears 

 to be endless to our human faculties. I have no wish to enter into 

 the question of the cosmic or telluric origin of life on the earth. 

 An answer to this question will at once decide whether the power 

 of reproduction possessed by these cells is in reality eternal or only 

 immensely prolonged, for that which is without beginning is, 

 and must be, without end. 



The supposition of a cosmic origin of life can only assist us 

 if by its means we can altogether dispense with any theory of 

 spontaneous generation. The mere shifting of the origin of life 

 to some other far-off world cannot in any way help us. A truly 

 cosmic origin in its widest significance will rigidly limit us to 

 the statement omne vivum e vivo to the idea that life can only 

 arise from life, and has always so arisen, to the conclusion that 

 organic beings are eternal like matter itself. 



Experience cannot help us to decide this question ; we do not 



D 



