PATHOGENICITY OF C. OVIS 459 



sometimes it has been apparently healthy. It is exceedingly difficult, from the 

 published reports, to determine whether these organisms have, or have not, played 

 any pathogenic role ; and in most instances they have not been studied in sufficient 

 detail to allow of any systematic identification or classification. We shall therefore 

 confine ourselves here to a brief description of the lesions produced by the named 

 species referred to above. 



C. ovis, often referred to as the Preisz-Nocard bacillus, (see Nocard 1889, Preisz 

 1894) causes caseous lymphadenitis in sheep and ulcerative lymphangitis in horses. 

 It differs sharply from C. diphtheria in that it is a pyogenic organism, and invades 

 the tissues. It resembles C. diphthericB in producing a filtrable toxin. 



Nicolle, Loiseau and Forgeot (1912) have carefuUy recorded the lesions met with in 

 guinea-pigs, which have died as the result of inoculating either Hving cultures of C. ovis 

 or bacteria-free filtrates siibcutaneously. In the former case, and where the dose of living 

 culture has been so adjusted that the animal dies about the 25th day, subcutaneous abscesses 

 develop in various situations during life. At necropsy, in addition to these superficial 

 lesions, small granulomatous masses are found in the Uver, spleen and lungs, and beneath 

 the parietal peritoneum. In the male guinea-pig similar lesions are found in the tunica 

 of the testis and epididymis Some of these lesions may have developed into large caseous 

 or caseo-purulent masses. 



When a guinea-pig is injected subcutaneously with a fatal dose of a toxic broth filtrate, 

 death occm-s within a few days, often in less than 24 hours, from an acute toxaemia. The 

 necropsy findings in such cases are entirely different from those described above. There 

 is a local, subcutaneous, inflammatory, gelatinous oedema at the site of inoculation, often 

 hsemorrhagic in character. The abdominal viscera are congested, and often show small 

 haemorrhages, particularly in the stomach, large intestine, and kidneys. The latter may 

 be almost black in colour. There is, however, no congestion of the adrenals, and no 

 exudation into the pleura. HaU and Stone (1916) give a very similar picture. 



Again, Petrie and McClean (1934) state that the efi"ect produced by the injection of 

 C. ovis toxin into the skin of a guinea-pig differs from that produced by the injection 

 of diphtheria toxin. The former gives rise to a definitely papular lesion, and if the 

 dose of toxin injected is large the lesions become pustular. According to Came (1940), 

 who defines the optimal conditions for toxm production, guinea-pigs, rabbits, sheep, goats, 

 pigs, horses, oxen, dogs and cats are all sensitive to its action. 



It has been shown by BuU and Dickinson (1935) that the pyogenic substance is largely 

 contained in the bacterial cells, as is suggested by the observations of NicoUe and his 

 colleagues, and that it is relatively thermostable. Suspensions of C. ovis, killed by heating 

 at 60° C. for 1 hour, no longer produce toxic death in susceptible animals, but they give 

 rise to sterile abscesses when injected in adequate dosage. 



It may be noted that the exotoxin of C. ovis is different from that of C. diphtherice. 

 Nicolle and his colleagues found that an antitoxin prepared against the former 

 gave specific protection against C. ovis toxin, whereas none was afforded by 

 diphtheria antitoxin. Dassonville (1907), Hall and Stone (1916), Minett (1922a, 

 h), and Barratt (1933) recorded some degree of protection by diphtheria antitoxin 

 against the toxin of C. ovis ; but the detailed study of Petrie and McClean (1934) 

 leaves little doubt that these effects were due to the fact that the sera of normal 

 horses may contain varying amounts of C. ovis antitoxin {C. ovis is a natural 

 pathogen of the horse) , and that the two toxins are immunologically quite distinct 

 from one another. 



Petrie and McClean have, however, found evidence of the existence of varieties of 

 diphtheroid bacilli that are, in respect of certain characters, intermediate between C. 

 diphtherice and C. ovis. These diphtheroids, aU isolated by various observers from the 



