THE PARASITIC EXISTENCE OF THE LOWER FUNGI. 627 



organisms, which require another kind of movement. 

 This fact can be utilised for obtaining, to some extent, 

 pure cultivations of yeast and of other fermentative 

 organisms. 



Nevertheless, the observations made by Na'geli do not 

 lead us to any certain conclusion as to the occurrence of 

 the fermentative action. With regard to the formation 

 of acetic ether, it is always conceivable that the same 

 bacteria produce both components, because we know that 

 the formation of alcohol is not limited to the yeast fungi, 

 and that glycerine, for example a body always present 

 in fermentation by yeast is split up, according to Fitz's 

 experiments, by bacteria with the formation of alcohol 

 and acetic acid. Objections may also be made to the 

 other facts brought forward by Niigeli, but, on the whole, 

 Nageli's view appears, at any rate for the present, to be 

 the best grounded, and hence the most probable, hypo- 

 thesis as to the act of fermentation. According to him 

 the fermentative act occurs in this way, that as the result 

 of the intramolecular activity in the protoplasm intense 

 conditions of movement are brought about, and that, on 

 the other hand, chemical molecules are present outside 

 the cells, which are set into active movement as the 

 result of these motions, so that the breaking up of the 

 molecule results. Those organisms are not capable of 

 setting up fermentation, in the plasma of which unsuit- 

 able and insufficient movements arise; only those 

 chemical substances can be broken up by the fermenta- 

 tion to which the movements can be readily communi- 

 cated. 



8. The Parasitic Existence of the Lower Fungi. 



The extension of the vital activity of the lower fungi Parasitism^ 



and symbiosis. 



which is of the greatest importance to us, is that they 

 can under certain circumstances grow as parasites on or 

 in the higher living organisms. It does not of necessity 

 follow that injury to the host is the consequence of such 



