146 MICRO-ORGANISMS AND DISEASE. [CHAF. 



that do exert isuch pathogenic properties are not at all de- 

 pendent on such acclimatisation, and are not ordinary moulds, 

 but a distinct species of aspergillus (Lichtheim), which grows 

 well at higher temperatures (38 48 C.), and the spores of 

 which under all conditions of growth are capable of producing 

 in rabbits the mycosis in question. 



(c) Penicillium. In this fungus hyphae, which are not 

 septate, grow out from the mycelium ; from the end of each of 

 these arise like the fingers of the hand a number of short 

 branched cylindrical cells, which give origin to chains of 

 spherical spores. 



The following two fungi belong to the order of fungi called 

 Phy corny cetes. 



(d) Mucor is characterised by this, that from the mycelium 

 hyphae grow out which are not septate, and at the end of these 

 a large spherical cell originates, sporangium, in which by en- 

 dogenous formation a large number of spherical spores are 

 developed ; the wall of the sporangium giving way, the spores 

 become free. 



(e) Saprolegnia ; colourless tubular threads, forming gela- 

 tinous masses on living and dead animal and vegetable matter 

 in fresh water. The cylindrical or flask-shaped ends of the 

 threads zoosporangia form in their interior numbers of 

 spherical or oval spores zoospores, possessed of locomotion 

 (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 aniheridio 

 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 a is 

 caused by this parasite. The zoospores of this salmon sapro- 

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

 The hyphae 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 



1 Proceedings of the Royal Society, No. 219, 18F2. 



