374 VETERINARY BACTERIOLOGY 



from most soils, and may be found to develop upon almost any 

 plate of medium exposed to the air. Only under exceptional 

 conditions are they pathogenic, but it is probable that the species 

 usually described as such are normally saprophytes that can, 

 upon occasion, proliferate in the tissues of the body and produce 

 disease. The fact that cattle become infected through the gums 

 or tongue, where the awns of certain grasses penetrate, that the 

 barley testers, who bite the barley grain to determine its brewing 

 quality, are most frequently infected among men in temperate 

 climates, that injuries to the feet of natives of certain tropical 

 countries (where no adequate protection is worn on the feet) are 



Fig. 161. Streptothrix (Actinomyces) coelicolor. Colony on agar. This colony 

 structure is quite typical of many species (Muller). 



frequently followed by local infections, and that Actinomyces have 

 been found causing infections in practically all domestic animals, 

 by one investigator or another is evidence of the wide distribution 

 of the members of the genus. The species to be described are 

 Actinomyces bovis and A. nocardii in cattle, A. caprcr in goats, 

 A. madurce, and A. eppingeri in man. 



The group, as a whole, may be characterized as consisting of 

 slender, branching organisms, which may develop into colonies 

 made up not only of threads but rods, cocci, and other cell forms. 

 Frequently, in animal ti^m-s :m<l sometimes upon artificial incd'ui, 

 the ends of the threads nuiy l*e dubbed. When grown upon the 

 surface of artificial media sonic forms develop aerial hyphae, 



