84 BACTERIOLOGY 



mould (Penicillium glaucum}, and black mould (Aspergillus niger) 

 are familiar examples. They may occasionally be associated 

 with disease, but the most important pathogenic moulds are 

 the group which cause Ringworm in man and animals, Favus 

 (Achorion schoenleini), Pityriasis Versicolor (Microsporon 

 furfur}, and certain rarer diseases of the skin and hair. 



Of diseases caused by the Ringworm group, some 80 or 90 per 

 cent, of the cases in children are due to the Microsporon audou- 

 ini, or small-spared variety, which invades the hairs and causes 

 them to break off short. The large-spored fungus contains two 

 groups, one variety of which especially attacks the interior of 

 the hairs and is therefore called Trichophyton megalosporon 

 endothrix : and another, found especially in animals and 

 communicated from them to man, grows chiefly on the outside 

 of the hairs, and is therefore known as Trichophyton mega- 

 losporon ectothrix. The former attacks the hair in older 

 children, and the latter usually attacks the face, nails, or 

 body, and may be found in adults. These fungi give charac- 

 teristic heaped-up, mould-like growths on culture, and grow 

 best on agar or gelatin to which beer-wort has been added, or 

 upon maltose-agar. 



The Thrush Fungus, Oidium albicans, which is often found 

 in the mouths of weakly children and produces white patches 

 on the tongue, gums, or cheeks, shows a mixture of a thread- 

 like mycelium and yeast-like bodies. 



Sporotrichosis is a rare condition found in the skin and sub- 

 cutaneous tissues, in which situations nodules form, break down, 

 and ulcerate. It is due to the Sporotrichon beurmanni, the 

 exact classification of which is still somewhat doubtful. 



The Pathogenic Protozoa 



The classification of these has been given upon p. 13, and of 

 late years an enormous amount of work has been done in con- 

 nection with organisms of this nature producing disease in man 

 and animals. The literature is very extensive, and we shall 

 content ourselves with the description of the parasites which 



cause Amoebic Dysentery, Sleeping Sickness, Spirochaetosis, 

 and Malaria. 



The Protozoa usually have a very complicated life-history, and 

 as a rule require more than one species of animal host in which 

 to carry out their complete developmental cycle. 



Ent amoeba histolytica. This organism is the cause of true 

 Tropical Dysentery, as opposed to the bacillary form described 

 on p. 73. It belongs to the Class Sarcodina or Rhizopods, 



