42 TAXONOMY 



convey the infection by the inoculation of pure cultures or pieces of diseased 

 tissue have not been successful. Microscopically the actinomycotic nodules 

 are seen to consist of nests of densely matted mycelium with the surface 

 layer of hyphae radiating outwards in all directions. The ends of the fila- 

 ments terminate in club-shaped swellings, whose appearance is characteristic 

 and unmistakable. They were formerly regarded as sporangia, but accord- 

 ing to more recent researches are the result of a swelling-up of the cell-wall, 

 or due to the deposit upon it of a gelatinous substance. They would there- 

 fore seem to represent rather a degenerative phase of the fungus than 

 organs of reproduction. 



A number of hyphomycetes are associated with various skin-diseases. 

 Whether they are strictly parasitic, or whether they occur outside the living 

 body in nature as simple mould-fungi, is uncertain. One of the commonest 

 forms is Trichophyton tonsurans^ the cause of a depilatory skin complaint 

 known as Herpes. The mycelium is found in the epidermal scales and 

 blisters, and grows well in artificial cultures, giving rise to chains of cylin- 

 drical gonidia. In Favtts, a skin complaint common to man and animals, 

 another hyphomycete is found, Achorion Schoenleinii. Some observers 

 think that this form should be split up into a number of distinct species, 

 others are content with one. Its morphology (in a botanical sense) has not 

 yet been fully investigated, but it belongs undoubtedly to the group of the 

 haplo- or hyphomycetes. 



The beautifully formed mould-fungi of the genus Aspergillus also 

 occasionally invade the human body. Besides the stalked heads with their 

 radiating chains of conidia, another kind of fructification, the perithecia, is 

 known. These perithecia show that Aspergillus belongs to the Perisporiaceae 

 (Ascomycetes), and for this reason some investigators have looked upon all 

 haplo- and hyphomycetes as imperfect ascomycetes. According to this 

 view we must expect to find some day the ascospores and asci of forms 

 like Achorion, Trichophyton, and countless others. This is undoubtedly 

 going too far. There undoubtedly exist simple moulds whose whole life- 

 cycle is comprised in mycelium and conidia. Aspergillus itself lives, 

 particularly in cultures, for years without forming ascus fruits. The conidia 

 of the mould-fungi retain their power of germination in the dried state for 

 very long periods. 



Three species at least of Aspergillus, A. fumigatus, A. niger, and 

 A.flavus (all with coloured spores), are possessed of pathogenic properties. 

 If a suspension of the spores be injected into a vein in the rabbit, mycelia 

 grow in all the organs of the body, and the abscesses formed are rapidly 

 fatal. Among birds, spontaneous infection is not uncommon, commencing 

 generally in the respiratory tract, the ear or the eye. Human beings, too, 

 are sometimes attacked, but the disease remains local, not spreading to 

 other parts of the body. In spite of these facts it is uncertain whether the 



