MODERNBIOLOGY 43 1 



therefrom that the sterility was due to lack of oxygen. At the beginning of 

 the nineteenth century the belief in spontaneous generation received fresh 

 impetus, not least as a result of the victory of Wolff's epigenesis theory; 

 Rudolphi believed in the spontaneous generation of tapeworms, and the 

 entomologists held the same belief in regard to parasites from the insect 

 world. It was chiefly, however, the increased knowledge of the Infusoria 

 that strengthened the belief in spontaneous generation; Ehrenberg's protests 

 died away unheard when the exaggerations in his description of the organi- 

 zation of these animals had been made manifest. 



Chemists on fermeriting 

 The idea of spontaneous generation received fresh support in the increased 

 knowledge of the fermenting process. Both Lavoisier and Berzelius had 

 studied the fermentation of alcohol and had sought to ascertain the process 

 of sugar-disintegration in alcohol and carbonic acid; the yeast that floats up 

 when it is brewed was believed to consist of albuminous elements, which 

 were separated upon the decomposition of the malt. This conception of 

 fermentation as a purely chemical process found support in the discovery of a 

 substance existing in malt that, when added to a solution of starch, converts 

 the starch into sugar. This substance was called "diastase," and similar 

 substances, "ferments" as they were called, were soon discovered in other 

 quarters: in saliva and intestinal fluids in man and animals, as also in many 

 places in the vegetable kingdom. Chemists believed that they now had in 

 their hands the substances that produce fermentation and similar processes, 

 and these chemical changes, in the course of which albuminous compounds 

 were formed as a by-product, also gave a clear indication as to the direction 

 in which the spontaneous generation of minute creatures might be looked 

 for; fermentation was in fact a part of the process of spontaneous generation. 

 Then there appeared, in 1836, the Frenchman Charles Cagniard de 

 Latour (1777-1859), an engineer by profession, with the assertion that the 

 yeast really consists of minute organisms and that it is their activity that 

 causes the fermentation. Shortly after this the question was taken up by 

 Schwann, who tried to demonstrate by experiment that putrefaction and 

 fermentation are processes which are not due to the oxygen in the air, but 

 rather to a special element that exists in the air and is destroyed by heating; 

 he boiled special easily decomposable organic substances and then brought 

 them into contact with air that had first passed through a red-hot pipe, 

 whereupon no chemical change took place, while there was a change if 

 ordinary air was allowed access to them. The leading chemists — Berzelius, 

 Wohler, Liebig — regarded these theories as a chimera, and they won the 

 day all the more easily because Schwann's experiments were, from the tech- 

 nical point of view, rather poor; other investigators repeated them and ob- 

 tained results quite different from those published by Schwann. Thus matters 



