BIOLOGY OF THE MICRO-ORGANISMS. 499 



were preferred as nutrient substances, and that therefore 

 the destruction of dead organic substances was chiefly 

 caused by fungi ; further, that carbonic acid could not in 

 any way be utilised either for assimilation or for growth. 

 But the physiological characters by means of which they 

 were able to play their peculiar role no longer appeared 

 to be so simple, and could no longer be defined in a few 

 words, but were made up of a number of processes 

 which required separate consideration, and which varied 

 markedly according to the species of the fungus and the 

 external conditions which surrounded it. Hence we 

 can no longer content ourselves with a general formula 

 if we would obtain an insight into the vital manifesta- 

 tions of the fungi; but we must proceed by the inductive 

 method, and seek to understand the life of the lower 

 organisms from a large number of individual observations 

 and experiments. In this place we must therefore enter 

 into a minute and detailed discussion as to the biology 

 of the fungi, and we must do this the more thoroughly 

 because this side of mycological investigation is of very 

 great importance for hygiene. 



The various biological phenomena which we observe 

 in the fungi can be subjected to experimental study in 

 the same manner as the vital phenomena of more com- 

 plex living beings, e.g., of animals or of the higher 

 plants. If we take the latter as our basis, we must 

 proceed from the more complex to the simpler, but it is 

 probable that many biological problems which have 

 proved insoluble in the case of the more complex organ- 

 isms, in spite of very numerous investigations, will be 

 much more readily solved in these simple beings, and that 

 thus at a later period the biology of the fungi will throw 

 light on the biology of higher plants, more especially 

 when we employ the methods of investigation which 

 have been found good in the case of the former. 



If we wish to study the tissue change of any of the 

 more complex organisms we generally attempt in the 

 first place, by a number of variations in our experiments 



