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 andto important special treatises, from which the reader will obtain further 
directions if he wishes to examine the somewhat profuse literature in greater detail’. 
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* 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®. 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. végétaux parasites qui croissent sur homme et les animaux vivants, 
Paris, 1858. 
Kuchenmeister, Die af u. in d. Körper d. Menschen vork. Parasiten, II, Leipzig, 1855. 
Steudener in Volkmann’s Samml. klinischer Vorträge, Nr. 38, Leipzig 1872. 
Baumgarten, Pathogene Mikroorganismen, I. (Deutsche Medic. Zeitung, 1884, 1). 
? Hoffmann in Bot. Ztg. 1868, p. 345, and the older works on the Saprolegnieae noticed above 
on page 145. 
5 Huxley in Nature, Vol. XXV (1881-1882), p. 437. See also the English reports in Just’s 
Jahresber. V, 96, 456, IX, 253. 
