CHAPTER VII. PHENOMENA OF VEGETATION. PARASITES. 375 



SECTION CV. Our knowledge of the Fungi which are parasitic on animals, 

 other than those contained in the groups which have now been considered, is so 

 small from the botanical point of view, that, with all due acknowledgment of the 

 medical interest of these plants and medical research, we can only touch upon them 

 briefly in this place. In doing this we shall refer especially to the medical works on 

 the subject and to important special treatises, from which the reader will obtain further 

 directions if he wishes to examine the somewhat profuse literature in greater detail 1 . 

 We cannot of course enter here into purely medical questions. 



The most important of the plants in question are the parasitic Saproleg- 

 nieae, the Fungi which cause diseases of the skin in warm-blooded animals, 

 men included, the Fungus of thrush or aphthae, and Actinomyces. Some 

 kinds comprised in this class are quite doubtful. 



Parasitic Saprolegnieae. Numerous cases are recorded in which living fish, 

 such as gold-fish, and other creatures living in water, as salamanders and frogs, were 

 attacked by Saprolegnieae, grew sick and died 2 . Destructive epidemics among 

 salmon have recently been reported, especially in the English and Scottish rivers, and 

 these epidemics are characterised by the development of Saprolegnieae 8 . We learn 

 from Huxley's investigations that the Fungus settles on portions of the skin of an 

 apparently healthy fish where there are no scales and sends mycelial or rhizoid- 

 branches through the epidermis into the inner layers of the skin, causing at first local 

 and then general disturbance of the system. Similar statements are made in other 

 cases. The examination of the Fungus has only shown that it is some form of 

 Saprolegnia. The formation of oospores, on which the determination of the species 

 depends, was either not observed or imperfectly described. Disregarding Huxley's 

 results for the moment, we may gather from the statements before us that the Fungi 

 in question are ordinary Saprolegnieae, which must have migrated to the living animal 

 as facultative parasites, since they usually vegetate as saprophytes (see page 141). If 

 this is so, there must have been some peculiarity in the fishes before they were attacked 

 by the Fungus, which is not found in the same fishes in the natural state ; there must 

 be some special reason for their being attacked by the Saprolegnia, perhaps 

 a disease of some other kind which we must not enquire further into here ; for the 

 ordinary species of Saprolegnia are so abundant in our streams and lakes, that if they 

 could attack the fish indiscriminately as facultative parasites, not one could possibly 

 be free from the Fungus. Direct experiments also have shown me that healthy gold- 

 fish may continue lively and free from the Fungus for months in water, in which 

 Saprolegnieae kept purposely in large quantities were forming an abundance 



1 The material collected from time to time will be found in the following publications : 



Ch. Robin, Hist. nat. d. vegetaux parasites qui croissent sur I'homme et les animaux vivants, 

 Paris, 1858. 



Kuchenmeister, Die an u. in d. Kbrper d. Menschen vork. Parasiten, II, Leipzig, 1855. 



Steudener in Volkmann's Samml. klinischer Vortrage, Nr. 38, Leipzig 1872. 



Baumgarten, Pathogene Mikroorganismen, I. (Deutsche Medic. Zeitung, 1884, i). 



* Hoffmann in Bot. Ztg. 1868, p. 345, and the older works on the Saprolegnieae noticed above 

 on page 145. 



3 Huxley in Nature, Vol. XXV (1881-1882), p. 437. See also the English reports in Just's 

 Jahresber. V, 96, 456, IX, 253. 



