CHAPTER XXI. 



PATHOGENIC FUNGI. 



In pathological bacteriology, besides the bacteria themselves, 

 higher organisms belonging to the group of fungi not in- 

 frequently claim attention. On the one hand, cultures may be 

 contaminated with the spores of the omnipresent terrestrial 

 forms growing in all decaying material, and on the other hand, 

 fungi of the same type are known to be the causal agents in 

 certain diseases. Before considering the latter, with which we 

 are more intimately concerned, we shall first give a short 

 account of the group of fungi as a whole and of some of the 

 common saprophytic forms. For this we are indebted to the 

 kindness of Professor Percy Groom. 



The overwhelming majority of fungi consist of tubular branched fila- 

 ments, termed hyphce, each of which has a thin continuous wall within 

 which are the protoplasmic and other contents. The whole body of the 

 fungus thus composed of hyphse is termed the mycelium. This may be 

 loose and web-like in texture, as in the case of common moulds, or may 

 assume the form of a compact skin or mass which is produced by the 

 copious branching and close interweaving of the hyphse, as in ordinary 

 toadstools. 



In the Phycomycetes, a lowly organised group of fungi, the hyphse are 

 typically continuous tubes devoid of any cross septa, excepting where re- 

 productive organs or cells occur ; whereas in the more highly organised 

 fungi, Mycomycetes, the hyphse are segmented by transverse walls. 



Inasmuch as fungi have descended from algae, which are mainly aquatic, 

 those fungi that are most alga-like betray in their life-history signs of the 

 aquatic mode of existence. Thus in a number of Phycomycetes the ends 

 of certain hyphae become shut off by a transverse wall. The terminal 

 chamber becomes swollen and its abundant protoplasm divides into a 

 number of cells, which, by rupture of the outer wall, escape as naked 

 ciliated swarm-spores. Each of these swims about in water (raindrops 

 and so forth), eventually clothes itself with a thin cell- wall, and, emitting 

 a hypha which grows and branches, develops into a. new plant. The 

 terminal organ within which these asexual spores arise is termed a 

 sporangium. In other types of Phycomycetes, for instance Mueor 

 mucedo (Fig. 162), the spores arising in the same manner inside a 

 sporangium acquire a cell-wall before rupture of the sporangium wall : 



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