At an early stage in the development of
bacteriological science it was clearly shown that
certain micro -organisms were pathogenic by virtue
of their diffusible poisons, now designated
The exact definition of exotoxins in the
light of recent knowledge has become a matter of
great difficulty. Formerly they were characterised
according to certain properties, their ready diffusibility in bacterial culture and filtrability from
the living organism, thermolability at 65 °C, high
toxicity in the animal body after an incubation
period following their injection, particularly their
selective action on certain tissues and tissue elements and their antitoxinogenic effect. Two toxins,
those of B. diptheriae and B. tetani exhibit all
these properties. Certain bacterial toxins which
may reasonably be classified among the exotoxins differ from these of B. diptheriae and B. tetani in certain important features and the characterisation
stated above is therefore too rigid. The most important character in the determination of an exototin
is now considered to be the ability to stimulate the
production of a specific antitoxin in the animal body.
It is suggested that this character may in some
measure be shared with the endotoxins. In the absence of any well defined characterisation of
exotoxins in general the toxin of each organism must
be characterised individually.
This also applies to the elaboration of
exotoxins. There is no proof they are invariably a
product of bacterial metabolism or are freed on
autolysis of the bacterial cell and there is no constant correlation between bacterial growth and toxin
production, some toxins, such as that of the classica"
B. welchii, being obtained from young actively growing cultures and others, for example that of B. diphtheriae, only from older cultures. It seems
probable that the mechanism of toxin production
varies with each type of bacterium.
Exotoxins also play parts of widely different importance in the mechanism of infection. Some
organisms, such as B. diphtheriae and B. tetani, have
low invasive powers and are pathogenic only by virtue
of their toxins while in the case of others, for
example the'Stáphylococci, the exotoxin is a less
dominant feature in the pathogenic mechanism of the
In this thesis special study is made of the
exotoxins of Staphylococcal and B. welchii strains.
In addition the absorption of these and V. septique
toxins from the alimentary tract is considered.