480 MUSGRAVE, CLEGG, AND POLK. 



Ziehl-Neelsen-Gabbett method. In older forms the segments are often 

 broken, the sheath-like substance not showing either in fresh or stained 

 specimens. The breaking up of the filaments produces great variety and 

 size of irregular forms; some of these may appear to be very much like 

 bacteria, but their true nature is easily established by laboratory methods. 

 The majority of these organisms may be stained by the aniline dyes, all 

 show Gram positive characteristics to a greater or less degree, and several 

 are as acid-fast as is the tubercle bacillus. 



Biologically certain species — both saprophytic and pathogenic — are 

 widely distributed in nature. They have been found on food stuffs — par- 

 ticularly cereals — in water, air, soil, etc. Zoologically they are found in 

 some insects and several animals, and in man. Cattle are the most fre- 

 quently infected of the animals, but rarer instances of the disease have 

 been reported for other species. 



Cultivation of these organisms is probably possible with all species, 

 although several authors have reported failures, and all observers have 

 noted the difficulty of obtaining a culture from the lesions in animals. 

 However, when adaptability to artificial media has once been secured, no 

 very great difficulty is found in keeping the culture. In general, it 

 may be stated that these organisms grow slowly on artificial media, 

 but that the cultures show most positive characteristics in the majority of 

 instances. In all there is a tendency to "pile up" on the medium rather 

 than spread over the surface. Pigment production of various shades is 

 a very common property, and this is more marked as a rule in glycerine 

 or glucose containing media. 



Resistance to physical, chemical, and other agents by these organisms 

 is rather great if we consider them to be non-spore bearing parasites, but 

 this resistance is not sufficient to permit us to consider that true spore 

 formation is present as it is understood for bacteria. 



Pathogenic character. — The pathogenicity of several species of 

 Streptothrix has recently been demonstrated by different workers, accord- 

 ing to the accepted bacteriologic rules governing such decisions. Other 

 members of the group appear to be saprophytes in that they do not produce 

 lesions in animals by the usual methods of procedure. There is also 

 considerable lack of uniformity in the results of animal experiments 

 with nearly all the pathogenic strains. However, working with monkeys, 

 our results have been more uniformly successful than those reported by 

 other observers, or than our own results with other laboratory animals. 

 The pathogenicity of this group of organisms seems to be influenced to 

 a certain extent by the same conditions which produce changes in the 

 virulence of bacteria. Not only may the virulence of some of these 

 species be increased by passage through susceptible animals, but with 

 the increased virulence differences in cultural results may be noticed. 

 These are shown principally in greater difficulty in securing growth, in 



