CHAPTER VII. PHENOMENA OF VEGETATION. PARASITES. 369 



Excrescences of the kind just described and local hypertrophies caused by Fungi 

 have been fitly compared with galls and have sometimes received that name. 



It is obvious that all these mycetogenous deformations and new formations and the 

 phenomena also of simple destruction are in direct causal connection with the process 

 of feeding the Fungus. In the latter case we see directly that the Fungus grows at 

 the expense of the parts which are destroyed, the substance of its own body constantly 

 increasing. In the case of tumours and hypertrophies there is often at first a striking 

 over-production of building material, as starch, and this is afterwards used for the com- 

 pletion of the development of the Fungus. In connection with this it often happens 

 that the parts deformed by the Fungus are also killed prematurely ; they die and are 

 decomposed sooner than the same parts when free from the Fungus and not deformed. 

 But every conceivable gradation is found in this respect in different species and some- 

 times in different individuals between the parasitism which quickly destroys its victim 

 and that in which parasite and host mutually and permanently further and support 

 one another, the relation which is most conspicuous in the formation of Lichens 

 and which Van Beneden 1 has termed mutualism. 



The phenomena here touched upon have not been submitted in any case to a strict 

 physiological analysis ; but the general nature of the enquiry is so obvious that it is 

 unnecessary to discuss it here. 



In the following summary of the chief phenomena and combinations which 

 actually occur we must keep the Fungi which live on animals distinct from those 

 which inhabit plants. 



FUNGI WHICH ARE PARASITIC ON ANIMALS. 



SECTION CIV. The Fungi which attack the bodies of living animals furnish 

 a series of instructive examples of the phenomenon of facultative parasitism (see 

 page 356). 



A number of species of Eurotium and Aspergillus (Sterigmatocystis), which all 

 occur chiefly as saprophytes and in that mode of life reach their full development, in 

 some cases even forming sporocarps, are able to migrate to the bodies of warm- 

 blooded animals and live at their expense, producing an abundance of typical gonidia, 

 but not, as far as we know, arriving at the formation of sporocarps. Their vegetation 

 causes or promotes a diseased state of the parts, known to physicians as mycosis. 

 Aspergillus flavus, A. niger and A. fumigatus, Eurotium repens and Aspergillus 

 glaucus are characteristic promoters of the disease of the human ear which bears the 

 name of otomycosis aspergillina'*. The Fungi find a nidus in the diseased (serous) or 

 excessive normal secretions of the skin, and their rapid growth causes inflammation 

 and excoriation of the parts. But in these cases, as Siebenmann urges, they do not 

 penetrate through the epidermis and are not developed in the healthy ear, so that they 

 virtually retain their saprophytic character, however decidedly they must be considered 

 to be promoters of disease. 



1 Animal Parasites and Messmates (Intemat. Scientific Ser. xix). See also De Bary, Die 

 Erscheinung d. Symbiose, Strasburg, 1879. 



2 Siebenmann, Die Fadenpilze Aspergillus, &c. u. ihre Beziehungen z. d. Otomycosis aspergillina, 

 \Viesbaden, 1883 ; many special treatises on the subject are enumerated in this publication. 



[4] Bb 



