500 BIOLOGY OF THE MICRO-ORGANISMS. 



on nutrition and tissue change, to determine the kind 

 and quantity of material which is taken up by them, 

 and to ascertain the normal relation of the other external 

 conditions which are necessary for the regular progress 

 of life; further, we investigate the fate of the materials 

 taken up, and how they are used in the body, also the 

 excretory products, and finally the functions of the 

 organs; and we are thus in a position to form an 

 approximate idea as to the alterations of the tissue and 

 of the energy which form the basis of the life of that 

 organism. 



We must study the biology of the lower fungi in a 

 similar manner. In the case of these also we must in the 

 first place ascertain experimentally the necessary condi- 

 tions of life ; we must learn what solid nutrient materials 

 must be supplied to the fungi, what role is played by 

 oxygen, and whether temperature, atmospheric pressure, 

 light, &c., exercise any noticeable influence on the growth 

 and the multiplication of the fungi. Where multiplica- 

 tion occurs by means of spores, we must ascertain what 

 are the conditions necessary for this act, and also on 

 what external circumstances the germination of these 

 spores depends. 



In the second place, it is necessary to study the results 

 of the life of the lower fungi. Among these we learn, in 

 the first place, the assimilation of the nutrient materials, 

 the tissue change in the cells, and at the same time the 

 various manifestations of energy for example, growth, 

 multiplication, and fructification; further, we find that 

 the fungi excrete various products of tissue change which 

 are of special interest ; and finally, that they exert under 

 certain circumstances two peculiar actions which require 

 more minute study, viz., fermentative action and the 

 production of disease. 



The study of the conditions of life also implies a dis- 

 cussion of the influences which are hurtful and destructive 

 to life. It is, however, advisable to consider the pheno- 

 mena of involution and of the death of the lower fungi 

 in a separate chapter, as well as the description of those 

 means by which we can interfere with the growth or life 



