INTRODUCTION. 3 



in virtue of, and as a manifestation of, the same power 

 whereby we are able to remember intelligently what 

 we did half an hour, yesterday, or a twelvemonth 

 since, and this in no figurative but in a perfectly 

 real sense. If life be compared to an equation of 

 a hundred unknown quantities, I followed Professor 

 Hering of Prague in reducing it to one of ninety-nine 

 only, by showing two of the supposed unknown quan^ 

 titles to be so closely allied that they should count 

 as one. I maintained that instinct was inherited 

 memory, and this without admitting more exceptions 

 and qualifying clauses than arise, as it were, by way 

 of harmonics from every proposition, and must be 

 neglected if thought and language are to be possible. 



I showed that if the view for which I was contend- 

 ing was taken, many facts which, though familiar, were 

 still without explanation or connection with our other 

 ideas, would remain no longer isolated, but be seen at 

 once as joined with the mainland of our most assured 

 convictions. Among the things thus brought more 

 comfortably home to us was the principle underlying 

 longevity. It became apparent why some living 

 beings should live longer than others, and how any 

 race must be treated whose longevity it is desired to 

 increase. Hitherto we had known that an elephant 

 was a long-lived animal and a fly short-lived, but we 

 could give no reason why the one should live longer 

 than the other; that is to say, it did not follow in 

 immediate coherence with, or as intimately associated 

 with, any familiar principle that an animal which is 

 late in the full development of its reproductive, system 



