THEWORKOFPASTEUR 20 



particles present sank to the bottom. They were washed with 

 sohent and then studied under the microscope. There were 

 always found thousands of organised bodies which differed 

 in no way from the common micro-organisms and their 

 spores. The presence of large numbers of organised bodies 

 in the ambient atmosphere had thus been demonstrated. 



Furthermore, Pasteur showed that these germs which are 

 present in the air can often initiate the growth of organisms. 

 First of all he repeated the experiments of Schwann with 

 some variations and improvements. The boiling of the 

 organic liquids was carried out in a round-bottomed flask 

 with a long dra^vn-out neck joined to a platinum tube which 

 was heated to red heat with a gas burner. Thus, the air which 

 was drawn into the flask when the liquid in it had finished 

 boiling passed through a red-hot platinimi tube in which all 

 the germs present in it w^ere sure to be destroyed. While 

 passing from the tube to the flask the air was cooled by a 

 stream of water. After it had been filled with air the flask 

 was sealed and in this state it could be kept indefinitely. 

 When the experiment was set up in this way the liquid never 

 decomposed and no micro-organisms were formed. However, 

 if the sealed neck of the flask was broken and a cotton plug 

 through which air had been passed was thrown into the liquid 

 contained in it and the neck was quickly sealed again, then 

 the liqiu'd soon became filled with moulds, bacteria and even 

 infusoria. This meant that the liquid had not lost its nutrient 

 capacity for micro-organisms and the germs which had been 

 present in the air and were collected on the cotton plug could, 

 in fact, easily develop in such liquids. 



Later Pasteur sterilised the air admitted to the flask 

 '^s'ithout heating it. For this purpose he relied partly on the 

 method of Schroder and Dusch. drawing the air through a 

 cotton-wool plug, and partly brought his own native skill 

 to bear on it. As usual, Pasteur half filled the round- 

 bottomed flask with the experimental liquid and then 

 softened the neck of the flask in a flame and drew it out. 

 The part which was drawn otit was bent into the shape of 

 the letter S. The contents of the flask were then boiled with- 

 out any further precautions. When a strong current of steam 

 issued from the extended neck of the flask the boiling was 



