ACTINOMYCOSIS, OR STREPTOTHRICOSIS 7I 



sheath of the radial filaments already mentioned, and are arranged 

 with their narrow extremities pointing inwards. They are not 

 generally present in man, and when present are often badly 

 developed ; they are much more common and more perfect in the 

 QX, where the disease is more chronic and pus-formation rare. 



The reason for this is, perhaps, partly that man is less resistant 

 against the organism, but probably the chief factor is the difference 

 in the fungus present. The organism in bovine actinomycosis is 

 the ray fungus, which is described above ; but in man there are 

 numerous species of fungus which can bring about infection and 

 cause the disease known clinically as actinomycosis : this disease 

 is therefore not a specific entity, due to a single cause, but a 

 group of allied diseases, just as suppuration is. The organisms 

 in question are all members of the genus Streptothrix, and consist 

 of long filaments of mycelium, which differ from the bacteria in 

 showing true branching and in breaking up into "chain spores," 

 resembling chains of cocci. The different species vary very 

 greatly in cultural characters, but there are also marked differ- 

 ences in the appearances met with in films of pus, etc. In what 

 may be regarded as typical cases, the nodules described above, 

 when flattened out and stained by Gram's method, show a central 

 portion consisting of a tangled mass of narrow mycelial threads, 

 some of which may show the degeneration into chain-spores, and 

 look like streptococci, whilst there may or may not be a peri- 

 pheral portion showing a radial arrangement (Plate II., Fig. 6, 

 which was drawn from a remarkably perfect specimen). These 

 colonies vary greatly in size, but do not usually fill up more than 

 half the field of an oil-immersion lens, so that it is best to search 

 for them in Gram specimens (not counterstained) with a low 

 power, and to turn successively the ^ and J^- on to any small 

 violet masses which may be seen. In some cases the fungus will 

 assume the form of threads in masses without any definite 

 arrangement, and in others the threads will be isolated ; in either 

 case it will usually be possible to find threads showing true 

 branching or chain spores, and this is sufficient for the diagnosis. 

 In yet others the bulk of the mycelium splits up into short lengths 

 greatly resembling bacilli, and when this happens the diagnosis 

 may be missed unless a careful search happens to reveal an 

 unbroken piece of mycelium (Plate IV., Fig. i). 



Cultures are usually difficult to prepare, and are not much help 

 in the diagnosis. 



