CHAPTER XI 

 PARASITIC FUNGI 



A PARASITE, as we have seen (p. 78) is an organism 

 which gets its food directly from another living 

 organism. Bacteria living in the intestines are scarcely 

 parasitic in the strict sense, though they actually live 

 within the body of another organism. Many of them 

 are harmless saprophytes living on the partly digested 

 food of the animal, but some cause diseases because 

 they produce toxins. Other bacteria, however, live in 

 the tissues, which they break down by means of the 

 enzymes they secrete, absorbing some of the products : 

 these are parasites in the strictest sense. 



Similarly with the fungi. Many are saprophytes : 

 some of these, however, are able to attack and break 

 down the tissues of living organisms (facultative para- 

 sites) ; others are exclusively parasites, and some are 

 strictly confined to one species of host. 



Fungi Parasitic on Animals. Though the great 

 majority of " zymotic " (germ) diseases of man and 

 the higher animals are caused by bacteria or by pro- 

 tozoa (unicellular animals), e.g. malaria, sleeping sick- 

 ness, dysentery, some especially skin diseases are 

 caused by genuine fungi which form a mycelium. 



The skin diseases generally known as ringworm are 

 among the commonest of these. These are caused by 

 several different kinds of fungi. Trichophyton, whose 



mycelium consists of chains of oval or rectangular 



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