INTRODUCTION 1 1 



This is, however, altogether a matter for experi- 

 ment. A highly complex organism may be quite 

 incapable of being transformed after a few generations 

 into other species, but after countless generations 

 under varying surroundings Nature would doubtless 

 promote those types which from accidental variations 

 were most suited to it ; and finally an organism 

 largely, if not totally, different from its primitive 

 ancestors may be the product of the long series of 

 survivals in ever-changing environments. Thus we 

 ourselves would not be regarded merely as the fittest 

 to survive in our own environment, had that environ- 

 ment remained throughout unchanged, but rather as 

 the descendants of the survivals in gradually changing 

 surroundings, so that we are merely the remnants, 

 so to speak, of all those that went before us, and 

 have inherited many qualities perhaps not altogether 

 the most suitable to our surroundings ; but neverthe- 

 less since we may possess on the whole counteracting 

 qualities more suited to the present environment than 

 the other progeny of our ancestors that have died 

 away, our survival may possibly not be so surprising. 



So also is it with microbes. They may differ 

 widely, nay even inexplicably so, from primitive 

 forms of life ; which we hope in the sequel to have 

 occasion to discuss. But in the long roll of ages 

 such bodies as may now appear to be living, 

 although the biologist may not be willing to 

 admit it, because so much simpler than the simplest 

 that he sees, these may still in countless ages have 

 been the direct descendants of such like forms as 



