ORGANISMS WHICH PRODUCE DISEASE 83 



Both in the tissues and on culture, the organism, as its name 

 Actinomyces or Ray-Fungus implies, tends to grow in a 

 radiate branching fashion. The filaments (see Frontispiece, 

 figs. 16 and 17), which are Gram-positive, often show a 

 dotted or granular appearance enclosed in a delicate sheath, 

 which may, especially in the lesions in cattle, undergo a 

 peculiar degenerative swelling known as "clubbing," this 

 change being especially found at the periphery of the 

 colonies. Calcification may ensue, with disappearance of the 

 filaments. Rounded or coccus-like bodies are also described 

 as occurring in the lesions. The filaments, especially in 

 culture, often show a tendency to break up into bacillus-like 

 elements, a point of interest in relation to certain phenomena 

 already described in connection with the acid-proof group of 

 bacteria (p. 76 et seq.). 



On culture, the streptothrix grows readily on potato and on 

 wheat-paste, the organism being in nature a parasite a form 

 of "smut" of cereals (wheat, barley, etc.), from which the 

 infection in cattle, and not infrequently in man also, is derived. 

 It also grows on agar and in gelatin and broth, especially if 

 glycerine be added. On a surface, the growth is raised dry, 

 tough, and brittle, and may resemble beeswax, or may be scab- 

 like. In gelatin, which is slowly liquefied, and in broth, there 

 is a tendency to grow in little fluffy balls, somewhat resembling 

 the granules found in the pus. 



Pathogenic Yeasts and Moulds 



The Blastomycetes or Yeasts (see Frontispiece, fig. 18) differ 

 from the Bacteria in their mode of reproduction, which in the 

 former is by gemmation or budding (instead of, as in the latter 

 by fission). In some of them, the Saccharomycetes, endospore 

 (ascospore) formation also occurs ; whilst in the Torulae, bud- 

 ding alone is seen. In man, the yeasts may produce certain rare 

 forms of ulcerative skin disease (Blastomycotic Dermatitis), 

 and even occasionally a generalised infection with the pro- 

 duction of tumour-like masses in the bones and organs. 



The Hyphomycetes or Moulds are characterised by the form- 

 ation of a felted network of threads the mycelium and by 

 the production of fruit-bearing hyphae which are familiar to 

 everyone as the velvety or cotton-wool-like appearance of a 

 mouldy surface, green or white or black as the case may be. 

 These aerial hyphae carry the sporangia in which the oval spores 

 are developed, sometimes preceded by a form of sexual repro- 

 duction. The common white mould (Mucor mucedo), green 



