SPONTANEOUS GENERATION OF MICROBES 27 



developed his theory of spontaneous generation, which is 

 fundamentally very reminiscent of the views of Needham. 

 Fermentation or decay of organic substances precedes each 

 manifestation of spontaneous generation. Only substances 

 forming part of living organisms can give rise to new life. 

 Under the influence of fermentation or decay the organic 

 particles of the corpse disintegrate but, having wandered 

 around for some time independently, they become united 

 once more by virtue of their inherent properties and thus 

 new living things are created. Pouchet considered that a 

 ' life force ' was a prerequisite for the development of living 

 things and therefore he never believed that living things 

 could arise de novo in mixtures of mineral substances. In 

 confirmation of his views Pouchet made a large series of 

 experiments in which he repeated the investigations of his 

 predecessors. In these he always got results in agreement 

 with his own ideas ; that is to say, micro-organisms always 

 developed in his organic liquids. 



Only about a hundred years separate us from the 

 experiments of Pouchet, but when one reads about these 

 experiments now one cannot help noticing how crudely and 

 messily they were carried out. Pouchet, for example, cate- 

 gorically denied the possibility that germs of micro-organisms 

 might have got into his infusions and solutions from outside 

 simply because " Joly and Musset carried out careful chemi- 

 cal analyses of the surrounding air ". But what could they 

 find out in this way even if thousands of bacteria and spores 

 were hovering around them? In just the same way Pouchet 

 asserted, without any foundation, that his original hay 

 inftisions certainly did not contain the germs of any micro- 

 organisms. However, we know that enormous numbers of 

 such germs are always present on the surface of hay and that, 

 on simple infusion of the hay with water, which is what 

 Pouchet did, these germs must certainly fall off into the 

 infusion in a perfectly viable state. This clearly occurred, 

 for when Pouchet placed his hay infusions in a warm place 

 for six days there appeared in them not only bacteria, but 

 also such highly organised creatures as infusoria, in the cells 

 of which there are digestive vacuoles, mouths and other very 

 complicated and specialised organs. It is quite clear to us 



