TEXT-BOOK OF BACTERIOLOGY. 15 



previous century, the wonderful experiments of the learned Abbe 

 Spallanzani had yielded decided proofs against the possibility of 

 spontaneous generation. Cautious and clever investigators, such 

 as F Schulze, Schwann, Schroder, and von Dursch, had still further 

 perfected these experiments and established their accuracy. But 

 the doctrine of spontaneous generation raised its head again and 

 again, and when it seemed to be fairly destroyed, it reappeared with 

 its old assertions and pretensions. 



Thus it required the influential personality of a Pasteur, his ener- 

 getic labors and his precise investigations to rid us once for all 

 of these traditional errors, and to settle the question so thoroughly 

 that it only now and then, quite stealthily and timidly, reaches us 

 like some voice out of ancient times. 



There were two facts in particular which led to and maintained 

 this belief in the self-originating powers of the bacteria. First, one 

 had no knowledge and no conception of the extraordinary powers 

 of resistance possessed by the lasting forms of the bacteria. 



We exposed fluid to a boiling heat for a quarter of an hour, and 

 supposed all life in it to be thereby destroyed. But we almost 

 always neglected to convince ourselves that the necessary tem- 

 perature really penetrated through all parts of the medium in 

 question. 



It has been found as a rule that this is not the case unless par- 

 ticular precautions are employed, and that the equable penetration 

 of the boiling temperature into fluids is by no means so easily at- 

 tained as was formerly supposed. But wherever the heat had not 

 properly penetrated spores could, under certain circumstances, find 

 a place of refuge, where they escaped destruction. One was not a 

 little astonished to see new bacterial vegetation reappear in such 

 liquids, even when the greatest care had been taken to protect 

 them against exterior pollution. Such growths were supposed to 

 have developed "of themselves" by "spontaneous generation," or 

 they were referred to as " atoms of nitrogen '' and other innocent 

 molecules, while, in fact, some spores that had escaped scalding, 

 were the cause of this mysterious process. Further, it was thought 

 necessary to suppose a generatio aequivoca, because we had no idea 

 of the wide distribution, the omnipresence of the bacteria. There 

 is, indeed, scarcely anything that is free from these minute, invisi- 

 ble, living forms. The great masses which surround us, the air, 

 the earth, the water, are as much stocked with them as are the 

 objects of daily use; the majority of our vegetables, our clothing 

 and our dwellings, our intestinal canal and the surface of our skin, 

 swarm with micro-organisms, and we only know one field which 



