CHAPTER L 

 THE PATHOGENIC FUNGI 1 



THE earliest demonstrations of microorganisms as the causes of 

 disease were the discovery of a fungus in the scutula of favus by 

 Schocnlein in 1839 and Langenbeck's discovery of the thrush para- 

 site in the same year. Later the work of Pasteur and his followers 

 showed the far greater importance of bacteria as disease-producers 

 and the study of these simpler forms has since been given greater 

 attention. We must, however, briefly consider a group of diseases 

 known as the mycoses which are due to infection by the fungi. 



In the broader sense the term fungi is used to include all 

 thallophyta (plants without stems, roots, or leaves) which are devoid 

 of chlorophyl or its analogues, and which consequently are limited 

 to a saprophytic or parasitic existence. In this sense the fungi form 

 a class of which the bacteria, or fungi which reproduce by simple 

 fission, are the simplest types. In the narrower sense the term is 

 applied only to forms which reproduce by means of spores. The 

 cells of these latter organisms are somewhat larger than those of 

 the bacteria and are usually enclosed in a well differentiated mem- 

 brane. They contain, as a rule, a demonstrable nucleus, granules 

 of various types and often vacuoles. Some fungi are unicellular, 

 as are the bacteria, but most are made up of many cells which are 

 interdependent and show some differentiation in form and function. 



Typical fungi are made up of cylindrical cells, joined into fila- 

 ments, from which smaller rounded cells called spores are developed. 

 From these two elements, filaments and spores, the fungi build up 

 a structure that differs immensely in complexity in the different 

 species. The unicellular types such as the common yeasts grow in 

 easily dissociated masses like bacteria and each cell combines the 

 functions of absorbing food-stuffs, of building them up into its own 

 substance and of reproducing new individuals. In the molds, which 

 represent simpler multicellular fungi, the filaments lie distinct in 



1 This chapter has been rewritten for us by Dr. J. G. Hopkins. 



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