INTRODUCTION 7 



brated for his cell-theory. He showed fifty years 

 ago that what we call 'putrefaction' is not the 

 result of death, but of life. The unpleasant smell 

 and the disintegration of dead bodies, whether of 

 plants or animals, is entirely due to microbes it is 

 the accompaniment of their digestion. If you 

 destroy all the microbes present by means of boiling 

 heat, and then prevent the access of new microbes 

 (which are blown about in the dust of the air), dead 

 bodies never putrefy. Supposing that by the fiat of 

 an omnipotent Being all microbes could be annihi- 

 lated, the earth's surface would soon be covered 

 with dead bodies remaining unchanged year after 

 year, century after century. The seas and lakes 

 would be choked with them, and we should have to 

 use them for paving our roadways and building our 

 houses. But worse than that, all the carbon and 

 nitrogen which living things use in turn in their 

 successive occupation of the earth's surface from 

 generation to generation, would soon be tied up. 

 There would be no food for the green plants : herbi- 

 vorous creatures would cease to exist. The con- 

 templation of these imaginable horrors gives us 

 some notion of the part played by microbes in the 

 order of nature.' 



