XV NUTRITION 167 



lively small part of the organism is set apart for repro- 

 duction, and it is only the reproductive cells thus formed — 

 spores or zygote — which carry on the life of the species : 

 the remainder of the organism having exhausted the 

 available food supply and produced the largest possible 

 number of reproductive products, dies. That is, all vital 

 manifestations such as nutrition cease, and decomposition 

 sets in, the protoplasm becoming converted into pro- 

 gressively simpler compounds, the final stages being chiefly 

 carbon dioxide, water, and ammonia. 



Mucor is able to grow either in Pasteur's or in some 

 similar nutrient solution, or on various organic matters such 

 as bread, jam, manure, &c. In the latter cases it appears to 

 perform some fermentative action, since food which has 

 become " mouldy " is found to have experienced a definite 

 change in appearance and flavour without actual putre- 

 faction. When growing on decomposing organic matter, as 

 it often does, the nutrition of Mucor is saprophytic, but in 

 some instances, as when it grows on bread, it seems to 

 approach very closely to the holozoic method. M. stolo- 

 nifer is also known to send its hyphae into the interior of 

 ripe fruits, causing them to rot, and thus acting as a para- 

 site. The parasitism in this case is, however, obviously not 

 quite the same thing as that of Opalina (p. 123) : the Mucor 

 feeds not upon the ready digested food of its host but upon 

 its actual living substance, which it digests by the action of 

 its own ferments. Thus a parasitic fungus such as Mucor, 

 unlike an endo-parasitic animal such as Opalina or a tape- 

 worm, is no more exempted from the work of digestion 

 than a dog or a sheep : the organism upon which it lives 

 is to be looked upon rather as its prey than as its host. 



It is a remarkable circumstance that, under certain con- 



