562 THE BACILLUS OF MALIGNANT (EDEMA 



Besson has shown that passage through guinea-pigs increases the virulence of 

 the organism. A bacillus is rapidly obtained of such virulence that less than one- 

 hundredth of a drop of a broth culture is fatal to guinea-pigs and rabbits in 8 hours, 

 and one drop is fatal to cats in 1215 hours. 



Babbits and white rats come next in the scale of susceptibility. Sheep, 

 goats and horses are also very susceptible ; the same is true of cats, a species 

 which is often erroneously said to be only slightly susceptible. Asses, small 

 birds, fowls and pigeons are less susceptible, next come dogs and finally oxen. 



Sewer rats are almost immune and only succumb to considerable doses of 

 very virulent viruses. 



2. Methods of infection. 



The bacillus of malignant oedema is a strict anaerobe and only multiplies 

 in the living tissues when introduced deeply beneath the skin or into the 

 muscles or peritoneal cavity. It does not lead to septicaemia when inoculated 

 into the veins and does not infect superficial wounds (Chauveau and Arloing). 

 The disease may be produced experimentally in animals in many ways. 



(i) By inoculation of a culture or infected exudate. Sub-cutaneous inocula- 

 tion is a very severe method of infection. Doses of less than O'Ol c.c. will 

 rapidly kill susceptible animals. 



(ii) By inoculation of the spores alone. Ancillary organisms. Besson has 

 shown that when the spores of the bacillus alone are inoculated into the sub- 

 cutaneous tissues of guinea-pigs and rabbits even in considerable doses 

 (4 or 5 million in the case of the guinea-pig, 14 million in the case of the 

 rabbit), they do not germinate but are rapidly phagocyted, and the animal 

 shows no lesion other than a small hard nodule at the site of inoculation 

 which disappears in a few days. 



Pure spores are easily obtained by destroying the toxin in broth cultures by heat. 

 Aspirate a few drops of a spore- bearing broth culture into a small glass tube, seal it 

 at both ends and keep it in a water bath at 80 C. for 3 hours. If the heated culture 

 be inoculated even in large quantities the animal suffers no ill- effects but if it be 

 sown in a fresh tube of broth a very virulent culture is obtained. An even more 

 simple method consists in using cultures which have been in the warm incubator 

 (37 C.) for several months; under these conditions the toxin disappears and the 

 spores alone remain. 



It is, however, only necessary to add a small quantity of some negatively 

 chemiotactic substance to spores to prevent the phagocytes fulfilling their 

 protective role to induce a condition of septicaemia. Thus, if a small 

 drop of lactic acid be mixed with the spores and the mixture be inoculated 

 the animal will die. A similar result is obtained if a small quantity of the 

 toxin of the bacillus, which possesses chemiotactic properties, be added to 

 spores : or if the latter be mechanically protected against the action of the 

 phagocytes as by enclosing them in a little piece of sterile filter-paper or in a 

 small cube of agar before introducing them beneath the skin of a guinea-pig. 



The septicaemia can be still more easily produced by spores free from 

 toxin if they be mixed with some other micro-organism, harmless in itself 

 but the secretions of which are negatively chemiotactic. Many organisms 

 found in soil can be used in this experiment as well as other species e.g. the 

 Micrococcus prodigiosus and the Staphylococcus pyogenes aureus. 



In the same way, traumatic injuries leading to death of the tissues (burns, 

 ligatures, etc.) lead to a diminished activity on the part of the phagocytes 

 and so favour the development of the spores. 



(iii) By inoculation of soil containing spores. The inoculation of a trace 

 of mud from the street or of garden soil sub-cutaneously beneath the skin of 

 a guinea-pig or rabbit often results in a fatal septicaemia. The development 



