230 BIOGENESIS AND ABIOGENESIS vm 



I propose to endeavour to follow this ancient 

 precedent, in a manner suited to the limitations of 

 my knowledge and of my capacity. I shall not 

 presume to attempt a panoramic survey of the 

 world of science, nor even to give a sketch of what 

 is doing in the one great province of biology, with 

 some portions of which my ordinary occupations 

 render me familiar. But I shall endeavour to put 

 before you the history of the rise and progress of 

 a single biological doctrine ; and I shall try to 

 give some notion of the fruits, both intellectual 

 and practical, which we owe, directly or indirectly, 

 to the working out, by seven generations of 

 patient and laborious investigators, of the 

 thought which arose, more than two centuries 

 ago, in the mind of a sagacious and observant 

 Italian naturalist. 



It is a matter of everyday experience that it is 

 difficult to prevent many articles of food from 

 becoming covered with mould ; that fruit, sound 

 enough to all appearance, often contains grubs at 

 the core ; that meat, left to itself in the air, is 

 apt to putrefy and swarm with maggots. Even 

 ordinary water, if allowed to stand in an open 

 vessel, sooner or later becomes turbid and full of 

 living matter. 



The philosophers of antiquity, interrogated as to 

 the cause of these phenomena, were provided with 

 a ready and a plausible answer. It did not enter 

 their minds even to doubt that these low forms of 



