44 LECTURE m. 



and heat to the infusions has been deemed to include all the condi- 

 tions required for the primary formation of the lower animal or of 

 vegetable organisms. The results in favour of such a view are, 

 however, explicable by supposing that due precautions had not been 

 adopted at the beginning of the experiment to exclude every animal 

 or germ capable of development in the infusion, or to gain satisfactory 

 assurance that the air subsequently admitted contained nothing of the 

 kind. The only experiment in which these difficulties appear to have 

 been fully overcome, is that in which the requisite apparatus was 

 conceived by Professor Schulze of Berlin. He filled a glass flask 

 half full of distilled water, in which were mixed various animal and 

 vegetable substances : he then closed it with a good cork, through 

 which were 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 violently. While the watery vapour was escaping 

 by the glass tubes, the Professor fastened at each end an apparatus 

 which chemists employ for collecting carbonic acid : that at the one 

 end was filled with concentrated sulphuric acid, and the other with a 

 solution of potash. By means of the boiling heat, it is to be pre- 

 sumed that every thing living and all germs in the flask or in the 

 tubes were destroyed ; whilst all access was cut off by the sulphuric 

 acid on the one side, and by the potash on the other. The apparatus 

 was then exposed to the influence of summer light and heat ; at the 

 same time there was placed near it an open vessel, with the same 

 substances that had been introduced into the flask, and also after 

 having subjected them to a boiling temperature. In order to renew 

 constantly the air within the flask, the experimentor sucked with his 

 mouth several times a day the open end of the apparatus, filled with 

 the solution of potash, by which process the air entered his mouth 

 from the flask after passing through the caustic liquid, and the atmos- 

 pheric air from without entered the flask through the sulphuric acid. 

 The air was of course not at all altered in its composition by passing 

 through the sulphuric acid in the flask ; but all the portions of living 

 matter, or of matter capable of becoming animated, were taken up by 

 the sulphuric acid and destroyed. From the 28th of May until the 

 beginning of August, Professor Schulze continued uninterruptedly 

 the renewal of the air in the flask, without being able, by the aid of 

 the microscope, to discover any living animal or vegetable substance ; 

 although, during the whole of the time, observations were made 

 almost daily on the edge of the liquid ; and when, at last, the Pro- 

 fessor separated the different parts of the apparatus, he could not 

 find in the whole liquid the slightest trace of Infusoria or Confervas, 

 or of mould ; but all three presented themselves in great abundance 



