4 BACTERIOLOGY. 



with greater persistency than Needham. Needham found that 

 animalcules readily developed \vhen meat infusion was boiled an 

 transferred to a well-stoppered flask, and he could only explain this 

 by supposing that they originated spontaneously from the material of 

 the infusion. In 1768 Bonnet strenuously opposed these conclusions 

 on purely theoretical grounds, and maintained that it was far more 

 probable that the ova of the animalcules were present in the infusions 

 or were suspended in the air enclosed in the flask. 



Spallanzani was the first to demonstrate by experiment the 

 correctness of Bonnet's arguments. It occurred to him to boil the 

 infusion in flasks, and to seal the vessels during the process of boiling. 

 As a result the flasks remained free from putrefaction, and 

 animalcules only developed when the infusion was exposed to the air 

 by making a hole in the flask. That Spallanzani's experiments 

 were reliable, and his conclusions correct, was evidenced by the fact 

 that his simple precaution led to great practical results, as Francois 

 Appert introduced, on this principle, the method of preserving meats, 

 vegetables, and other provisions. 



The disciples of Needham nevertheless brought forward counter 

 objections. Treviranus urged that a certain quantity and quality of 

 air was necessary for the spontaneous development of these infusoria, 

 and that by sealing the flasks, too small a quantity of air was in 

 contact with the infusion, and, further, that this air had become 

 changed in quality by the process of boiling. 



Spallanzani argued against these objections, but did not support 

 his opinions by further experiments, so that the question remained 

 for a time undecided. 



In 1836 Francis Schulze devised an experiment which brought 

 still further evidence against Needham's theory. Schulze filled a 

 glass vessel half full with distilled water and different animal and 

 vegetable substances. This was plugged with a doubly-bored cork, 

 and through each perforation a glass tube was introduced, bent at 

 a right angle. On boiling the flask, steam issued freely from each 

 tube, and all parts were thoroughly sterilised. Each tube was then 

 connected with a bulbed tube, one bulb containing concentrated 

 sulphuric acid and the other a solution of potash. Fresh air was 

 drawn into the flask by aspiration, and this was deprived of any 

 germs which might be present by its passage through the sulphuric 

 acid. The result was that the infusion remained without any 

 development of micro-organisms. When, on the other hand, air was 

 admitted without first being drawn through the sulphuric acid, the 

 n asion in a short time teemed with animalcules. In other words 



