The aim of the study described in this thesis was to obtain information about the chemical nature of the immunizing antigen of the vaccines against blackleg disease and the mechanism of the immunization. A literature study revealed the existence of much controversy about the reactions caused by Cl. chauvoei germs and toxins. Though the results of serological
experiments carried out by various investigators led to the
accepted theories about the relationships between homologous
lethal toxins and haemolysins~ and between the haemolysis
and other reactions of the two different species
Cl. chauvoei and Cl. septicum, a comparative chemical
study of the toxins had not yet been carried out. A preliminary investigation showed that the soluble immunizing antigen from the Cl. chauvoei cultures had the character of proteins. This was revealed by the loss of activity when pepsin and trypsin were allowed to act upon the antigenic solution and further by the
influence of acid and heat upon the antigenic potency.
No lethal activity was found in the filtrates of Cl. chauvoei (strain 64) cultures; instead we detected a
haemolysin and a hyaluronidase which were also both
heat-labile. The isolation procedures for the antigen and
haemolysin relied on precipitation with ammonium sulphate
and on chromatographic methods.