4 THE THEORY OF SPONTANEOUS GENERATION 



4. Spallanzani's Experiments. 



Of the two hypotheses forming the basis of Needham's deduction, the 

 accuracy of the second, i.e. that relating to the exclusion of outside germs, was 

 examined first. Some twenty years after the appearance of the English theory, 

 the Abbe SPALLANZANI (I.) published a dissertation in which he combated the 

 doctrine of spontaneous generation. In this work the Italian divine detailed 

 the experiments which had led him to the conclusion that a development of the 

 animalculsB in question, in an infusion maintained at boiling-point for three- 

 quarters of an hour, was only possible provided air, which had not been pre- 

 viously exposed to the influence of fire, had been admitted. This position was 

 also maintained by Spallanzani in a second treatise (II.). 



Nevertheless, the supporters of the spontaneous generation theory were still 

 far from regarding their cause as lost. They characterised these experiments as 

 inconclusive, since (so they said) " by the immoderate heat Spallanzani chose to 

 employ, the air in the vessel is so unfavourably changed, and rendered so 

 unsuitable for the maintenance of life, that it is no occasion for surprise that 

 all development was lacking." This objection was curtly rejected by Spallanzani, 

 but an experimental confutation was only ariived at much later. The next step 

 in this direction was accomplished in 1836 by 



5. Franz Schultze's Experiment. 



In order to avoid under-estimating the value of the very short treatise (I.) 

 published by this investigator, regard must be had to the influence attained by 



Chemistry in all branches of 

 natural science during the sixty 

 years that had elapsed since 

 Spallanzani's demonstration, an 

 influence which will be eluci- 

 dated, in so far as it refers to 

 the theory of Fermentation, in 

 subsequent sections. The idea 

 that ordinary air acts as an 

 inducer of fermentation or 

 putrefaction by reason of its 

 content of living germs was 

 first called into existence by 



FIG. i. Franz Schultze's Experiment. Schultze. 



He described his experi- 

 ment as follows: "I filled a glass flask half full of distilled water (Fig. i), 

 with which I bad mixed various animal and vegetable substances, and closed 

 it with a sound cork, through which were passed two tight-fitting glass 

 tubes bent to elbow joints. 1 next placed it in a sandbath and applied heat 

 until the water boiled briskly, so that all parts were exposed to a temperature 

 of 100 C. Whilst the hot water vapour was still issuing from the two tubes, 

 I attached to the end of each an apparatus employed by chemists, in the 

 course of organic analyses, for the absorption of carbon dioxide. That on the 

 left-hand side was filled with concentrated sulphuric acid, the other with a 

 solution of potassium hydroxide." After cooling the apparatus, air was drawn 

 through twice every day during the ensuing two months, in such a manner that 

 it had to pass through the sulphuric acid before entering the flask. The results 

 confirmed the expectations of the investigator, the contents of the flask when 



