446 Immunization of Animals Against Bacterial Disease
that the capsule is frequently associated with virulence and hence with immuno-
logical problems. Pneumococci, which are responsible for lobar pneumonia
in the human subject, are capsulated and there are many antigenic types.
These capsules are of a polysaccharide nature and they determine the antigenic
behaviour of the organism and are therefore of prime importance [Avery and
Goebel, 1933]. The capsule of the anthrax bacillus is also of importonce but is
protein in nature [Tomcsik and Ivanovics, 1936]. A large amount of
chemical investigation is involved in recent work on bacterial antigens and
the corresponding immunity. Chemical fractions capable of inducing an active
immunity have been isolated from some of the enteric group of bacteria
[Boivin and Mesrobeanu, 1935, 1936 ; Raistrick and Topley, 1934 ; Topley et al.,
1937], from some streptococci [Stamp and Hendry, 1937] and from the bacillus
of whooping cough [Cruickshank and Freeman, 1937]. An important advance
even on these is announced by Goebel [1939] who has produced a synthetic
antigen capable of inducing immunity to Type III pneumococci.
As knowledge extends, the crude immunological reagents now used will be
replaced by purer products and there should follow an increasing control over
infective diseases. One of the crudest products is the ' living vaccine ' which
is used in swine erysipelas, anthrax and Brucella infections. Such vaccines
are used where fundamental knowledge of the pathogenesis of bacteria is vague
or lacking and such vaccines should not be used if they can be avoided. In
addition to the possible danger to the animal injected, there is the probability
of perpetuating a disease, by increasing the number of carriers, and all freshly
introduced stock have to be protected by similar means. In some cases there
is a potential danger to the human subject and in addition there is no control
of a ' living vaccine ' after it has been introduced into an animal.
Some years ago, Ramon noted that horses which were being immunized
produced a better product when an abscess was formed at the site of inocula-
tion. He and his colleagues introduced tapioca [Ramon and Descombey,
1927, Nattan Larrier et al., 1927] or some chemical substance such as trypar-
samide into their vaccines because a local reaction was formed, absorption was
slower and a better immunity resulted. Tapioca is still used in Poland as an
addition to tetanus toxoid for the immunization of army horses, but in some
countries other substances such as saponin, lanolin and alum have been incor-
porated. A well-known method is to add potash alum and the toxoid becomes
loosely attached to the aluminium hyroxide precipitated [Glenny et al., 1926].
Alum-precipitated diphtheria toxoid is widely used in the active immunization
of children and alum-precipitated tetanus toxoid in man and animals. The
foot-and-mouth disease vaccine recently described by Waldmann [1938] in
Germany has an addition of aluminium hydroxide for a similar purpose.
THE ASSAY OF BACTERIAL PROPHYLACTICS
Before any vaccine is issued for use it is of course essential that it
be tested for its safety and efficacy. Although vaccines may be assayed
by in vitro methods such as the number of bacterial bodies in a