56 BACTERIA. 



that the germs of micro-organisms, or eggs, as he termed 

 them, might exist on the walls of the vessel, on the material 

 of which the infusion was made, or suspended in the air 

 within the vessel. To get rid of these germs from the vessels 

 he heated the latter on the fire, then filling them rapidly 

 with his infusions he allowed them to cool, and sealed them 

 hermetically, but he still found that after a few days a 

 number of organisms made their appearance. Could the 

 organisms have got in along with the air during the process 

 of cooling ? 



To set this question at rest he made a number of infusions in 

 hermetically-sealed flasks, and boiled them for a whole hour, 

 with the result that in flasks so treated no organisms made 

 their appearance : if, however, the sealing was in any way 

 interfered with, organisms soon made their appearance, and 

 he concluded that living germs were necessary for the 

 development of putrefactive organisms. This fact once 

 established, the whole question was much simplified, and the 

 principle on which it rested was soon utilized in Paris and else- 

 where in the methods adopted for insuring the preservation 

 of various food stuffs methods which, with few modifications, 

 have been handed down to the present day. It was of course 

 objected that Spallanzani had shut out air from his vessels, 

 or, that he had so altered the constitution of the air which still 

 remained, that it was not possible for these minute organisms 

 to develop in it. This objection was met in 1836 by F. 

 Schulze, who put the question to himself, "If the access of 

 atmosphere, light, and heat, to substances in flasks included 

 of itself all the conditions for the primary formation of 

 animal or vegetable organisms." To prove that this was not 

 the case, Spallanzani's conditions of absolute freedom from 

 germs capable of development in the infusion must be 

 obtained, and, secondly, air must be admitted to this infusion 

 in considerable quantities ; but the air so admitted must be 

 perfectly free from germs. 



Schulze proceeded as follows : he filled a flask half full of distilled water, 

 to which he added various animal and vegetable substances. He gives the 

 following description of the further methods of procedure : " I then closed 

 it -with a good cork, through which I passed two glass tubes bent at right 

 angles, the whole being air-tight ; it was next placed in a sand bath and 

 heated until the water boiled, and thus all parts had reached the temperature 

 of 212 F. While the watery vapour was escaping by the glass tubes I 

 fastened, at each end, an apparatus which chemists employ for collecting 



