BIOLOGY OF THE MICRO-ORGANISMS. 497 



more apparent since we have learned that a scarcely 

 noticeable oxidation occurs when organic materials and 

 the oxygen of the air are simply in contact with each 

 other at the ordinary temperature, and that on the con- 

 trary it is the living cells which furnish the necessary 

 conditions for a rapid destruction and oxidation of 

 organic materials. Further, it must be pointed out that 

 the substance of the dead animal body must also be ex- 

 posed to destructive influences in the same manner as 

 dead vegetable materials ; for we also see in the case of 

 animal organic materials that the atmospheric oxygen 

 alone is relatively powerless to convert these compounds 

 into carbonic acid, ammonia, and water. 



This dangerous gap in the constant process of re- The fungi 

 generation in nature is made good by the action of the rganic P ( 

 lower fungi. They form the necessary factor which ^^^nder^ 

 renders a rapid destruction and oxidation of dead organic them of use 

 materials, whether of animal or vegetable origin, possible, 

 and which reproduce the simple carbon and nitrogen 

 compounds which are necessary for the nutrition of 

 living and growing plants. The fungi are able to per- 

 form this role because they do not, like the chlorophyl- 

 lous plants, utilise the energy of the sun, nor obtain 

 their nutriment from carbonic acid and ammonia, but, 

 like animals, feed on the complex chemical compounds, 

 and utilise the energy so liberated for the performance 

 of their functions. They are the better able to do this 

 on account of the wide limits within which their ex- 

 ternal conditions of existence can vary without injury; also 

 on account of their extraordinarily rapid multiplication, 

 for which they use up a considerable amount of nutrient 

 materials in a short time ; and further, because under 

 such circumstances they only utilise a relatively small 

 proportion of the nutrient materials for their own growth, 

 while a much larger proportion is decomposed by their 

 peculiar fermentative actions, and thus prepared for 

 further oxidation. Lastly, it is as it were only a slight 

 alteration of their function when they at times settle as 

 parasites on living plants and animals, and lead to their 

 destruction by breaking up very rapidly the organic con- 



32 



