PA THOGENICIT Y 379 



Pigment formation is characteristic of many of the aerobic species, the usual 

 colour being some shade of pink or brown. 



Antigenic Structure. — Colebrook (1921), working with three strains of the 

 Wolff-Israel type, found that their agglutination reactions differed. Aoki (1936^/, b), 

 using agglutination and complement-fixation reactions, found that 6 anaerobic 

 strains all fell into one group, but that 19 aerobic strains fell into eight different 

 groups. The careful observations of Erikson (1940) have shown that by agglutina- 

 tion, aided when necessary by absorption of agglutinins, the anaerobic species 

 can be divided into (1) a group containing strains of human origin, which are 

 antigenically homogeneous though differing in their degree of agglutinability, and 

 (2) a group containing strains of bovine origin, likewise homogeneous, but with 

 much less power of giving rise to antibodies in rabbits. It must be noted, how- 

 ever, that all of Erikson' s bovine strains were of Australian origin ; whether 

 European strains behave similarly is not known. 



Pathogenicity. — The anaerobic Wolff-Israel type appears to be responsible for 

 actinomycosis in man and cattle. The aerobic types are mostly saprophytic, but 

 occasionally they are able to give rise to chronic granulomatous lesions in man 

 and other animals. 



For laboratory animals both types have a low pathogenicity. Inoculated in 

 a large dose subcutaneously into rabbits they give rise to a circumscribed abscess, 

 which may persist for weeks or months ; in the pus Drusen may often be found 

 (Hassegawa et al. 1938). Intraperitoneal injection of the Wolff-Israel type into 

 guinea-pigs and rabbits may give rise to small nodules containing typical granular 

 pus, but the lesions are neither extensive nor fatal. By the repeated inoculation 

 of massive doses intravenously Slack (1942) was able to kill rabbits in 6-10 weeks, 

 and to demonstrate post mortem the presence of macroscopic or microscopic 

 abscesses and focal necroses in the lungs and liver, sometimes containing granules 

 with hyalinized clubs. The acid-fast members of the aerobic group, such as 

 Actinomyces asteroides, are more pathogenic. Injection of this organism by the sub- 

 cutaneous, intravenous, or intraperitoneal route leads to a progressive fatal infec- 

 tion of guinea-pigs and rabbits in 5 days to 4 weeks. Post mortem, small tubercles 

 are found scattered throughout the organs, being especially numerous in the lungs, 

 liver, and spleen (Eppinger 1891, MacCallum 1902). Microscopically these nodules 

 contain tangled filaments, sometimes arranged in the typical ray form. 



Variation in Actinomyces bovis. — Not all the anaerobic strains isolated from 

 actinomycotic lesions conform to the description that we have given. Lentze 

 (1938) pointed out that in certain cases an anaerobic bacillus of more diphtheroid 

 appearance might be found, differing in its morphological, cultural, biochemical 

 and antigenic characters from the classical Wolff-Israel type. He designated 

 the new form as the S and the old as the R form. Erikson (1940), however, rightly 

 objects to this terminology, and since the majority of the new strains are of animal 

 origin, refers to Lentze's S and R forms by the terms bovine and human respec- 

 tively. Whether these different forms are stable varieties, analogous to the bovine 

 and human types of the tubercle bacillus, must await further observation. 



The chief differential characters of strains of bovine origin are as follows : — 

 The mycelium undergoes fragmentation very rapidly so that rod forms are pre- 

 dominant ; extensive ramification is rare ; growth is scanty ; the colonies are 

 smoother, softer, have an entire edge, and are not adherent to the medium ; aerial 

 hyphse are not formed, as they may occasionally be by the classical form (Erikson 



