18 



INTRODUCTORY HISTORICAL REVIEW 



instrument was evidently very poor and did not lead to any important 

 discoveries. It was not until the seventeenth century that the micro- 

 scope really gained importance, when Antony Van Leewenhoeck, the 



FIG. 1 



Experiment of Schulze: Forcing air through sulphuric acid. (Lafar.) 



true father of microscopy, succeeded in producing a fairly good instru- 

 ment with magnification up to 150 diameters. He discovered the 

 spermatozoa, and numerous small live organisms in saliva, stagnant 

 water, fermenting and decomposing fluids, and organic materials. 



FIG. 2 



Experiment of Schwann: Heating air to make it sterile. (Lafar.) 



After these small organisms had been studied for a number of 

 years the theory was promulgated, particularly by Van Helmont and 

 Needham, that these forms of life arose by spontaneous generation 

 in such fluids as meat infusion, etc., even after they had been boiled. 

 This view was contested by Spallanzani, who showed that when a meat 

 infusion had been boiled three-quarters of an hour, and kept from 



