HARVEY AND MILTON 223 



circulation of the blood, declared, as a general law, that 

 every living thing is born from an egg. During that 300 

 years his conclusion has been examined and modified, 

 corrected and expanded, and the microscope has at last 

 enabled us to see and follow the excessively minute 

 particles and structures by which sexual reproduction is 

 effected. Harvey's dictum was a step in advance when it 

 was made, for previously the belief was current that living 

 things were " bred " in all sorts of queer ways. It was 

 supposed that the putrefying flesh of a dead animal 

 actually was converted by a sudden process into maggots, 

 and that rotten wood would breed, out of its own sub- 

 stance, ship's barnacles and even young geese and mice — 

 an opinion contested only 200 years ago by Sir Thomas 

 Browne ! No difficulty was felt in admitting that whole 

 swarms of insects, fishes, and even herds of larger beasts 

 were spontaneously generated from mud, from putrid 

 matter, or from the waters of the sea. That, indeed, was 

 the popular notion set forth by the poet, John Milton, as 

 to the mode in which living things were " miraculously " 

 brought into existence at the beginning of things by the 

 " fiat " of the Creator. What more probable than that 

 such a creation should still be, here and there, at work ? 

 However, not three centuries ago, actual experiment 

 gradually convinced the learned that maggots are bred in 

 a dead body only from the eggs laid by parent flies, as 

 shown by the Italian Redi in 1668 who found that no 

 maggots were bred when he simply excluded the flies from 

 access to the dead body by covering it with wire gauze, 

 but that the blow-flies swarmed on the gauze and vainly 

 laid their eggs on it ! It was only gradually recognised 

 that birth by means of eggs or germs extruded from 

 parental organisms of the same history and character as 

 their offspring is the explanation of all such swarms of 

 flies, worms, and even mushrooms and moulds as had 



