100 HISTORY AND SIGNIFICANCE OF SCIENCE 



Spontaneous Generation. This theory, although restricted 

 to the origin of microscopic organisms, was actively cham- 

 pioned. Redi had show (1668) that insect larvae, which had 

 been supposed to arise spontaneously in decaying flesh, 

 actually arose from the eggs of parent forms, as did larger 

 animals like the birds and reptiles whose eggs are of con- 

 spicuous size. It was, of course, recognized that the higher 

 plants developed from seeds. The discovery of microorgan- 

 isms (c. 1675) reopened a question which might otherwise 

 have been regarded as settled. Admitting that larger ani- 

 mals and plants arose from parents, and not by a process 

 of spontaneous generation, it might still be maintained that 

 simpler and microscopic types originated without the inter- 

 vention of living matter. The early investigators beheld 

 their infusions teeming with microscopic organisms that 

 appeared literally over night. Some naturally believed 

 there could be no other explanation of this sudden appear- 

 ance but that of spontaneous generation. Although the 

 work of Spallanzani (1775) and others during the eighteenth 

 century produced evidence against this spontaneous origin 

 of living bodies, it was impossible to secure a conclusive 

 verdict until the cell-theory was established and until com- 

 plete life-cycles for representative microscopic forms were 

 made known toward the middle of the nineteenth century. 

 The later eighteenth century was concerned with this 

 problem, as it was with the broader generalizations in other 

 scientific lines. In view of the absence of a cell-theory, it is 

 perhaps remarkable that the advocates of spontaneous 

 generation were not more numerous. 



In medicine, the final steps, which divorced the treatment 

 of disease from superstitions such as belief in demoniacal 

 possession and in the visitations of Providence, were taken 

 during the eighteenth century. This happened in spite of 

 popular survivals of such beliefs. Disease was increasingly 

 acknowledged to be an abnormal bodily state, and as such to 

 be subject to investigation by science. Jenner's discovery of 



