486 MICRO-ORGANISMS AND DISEASE [chap. 



tion (one flagellum at each pole) and which finally escape 



from the threads. These zoospores after some time become 



resting, surround themselves with a membrane, and finally 



germinate into a cylindrical mass which becomes transformed 



into the mycelium. Besides this asexual there is, however, 



a second or sexual mode of fructification, consisting in this : 



At the end of a mycelial thread a cell grows up into a 



spherical large ball, the oogonium. From the same thread, 



thin threads — antheridia — grow towards the oogonium, with 



the protoplasm of which they merge. This latter then 



differentiates into a number of spherical masses, the oospores, 



which become invested with a membrane. These become 



free and then germinate and grow into a mycelium. 



Saprolegnia grows on the skin of living fish, and causes 



here severe illness often terminating in death. Thus the 



salmon disease, as Professor Huxley has shown, ^ is caused 



by this parasite. The zoospores of this salmon saprolegnia 



are, however, as Huxley has shown, as a rule non-motile. 



The hyph» of the fungus traverse the epidermis in the 



diseased patches of the salmon, and they bore through the 



superficial layer of the derma, a stem-part being situated in 



the epidermis, and a root-part in the derma ; each of these 



elongates and branches out. " The free ends of the stem- 



hyphae rise above the surface of the epidermis and become 



converted into zoosporangia, more or fewer of the spores of 



which attach themselves to the surrounding epidermis and 



repeat the process of penetration." In saprolegnia associated 



with the salmon-disease Professor Huxley observed only the 



asexual mode of fructification. 



(/) Actinomyces, or ray fungus. — Bollinger ^ first showed 



that various tumours in cattle leading to chronic suppuration, 



^ Proceedings of the Royal Society . No. 219, 1882. 

 2 Centralbl.f. d. med. IViss., 1877, No. 27. 



