h histological study was made on tonsils from porcine foetuses
in late gestation up to aged adults to provide a concept of normality
as a background to later experimental studies. In late gestation.
lymphocytic follicles were frequently observed in the tonsils.
!'erminal centres were noted by four weeks of age, thereafter
increasing markedly in number, size and activity. The interfollieular
lymphoid tissue developed in cellularity, presenting lymphocytes,
macro;ha7es, plasma cells and large pyroninophilic cells by one month
of age. Germ -free and dibiotic animals of this age showed an essentially similar tonsillar structure. In pigs up to one year of
age there was little variation in this pattern but from then on germinal centre activity decreased markedly. Senile changes
included atrophy of the branching tonsillar crypt system and an increase in the connective tissue stroma, replacing much of the
To define the afferent and efferent pathways to the palatine
tonsils, non-infective studies employing vital dyes ,:ere carried out.
Intra-vital dye injections failed to illustrate any afferent route
to the tonsils from adjacent areas, while confirming the tonsillar
efferent lymphatic drainage to the submandibular lymph nodes.
Topical application of India ink to the oral surface of the tonsils
defined an afferent route through the tonsillar crypt epithelium to
the lymphoid parenchyma. Ink was distributed throughout the inter-follicular tissue, occasionally within germinal centres, and later
in trabeculae and the capsule from which the efferent lymphatics
take origin. Examination by electron-microscoy revealed that the
tonsillar crypt epithelial cells participate in phagocytosis.
Infective studies with Streptococcus suis were carried out to
investigate the role of the palatine tonsils in the pathogenesis of
piglet streptococcal meningitis and arthritis caused by this
organism. Application of :'tree. suis to the oral surface of the
tonsils produced clinical disease in one of four piglets infected at
ten days of age; inapparent infection occurred in the other three in
which the organism was confined to the tonsils and their drainage
lymph nodes. :'tree. suis or its antigenic breakdown products,
specifically identified by immurofluorescert microscopy. were located
in the tonsillar crypt lumina, epithelium, interfollicular tissue and,
rarely, in germinal centres, of all four infected piglets.
Histological examination failed to reveal any abnormalities of the
tonsils. In a second experiment, phagocytosis of bacteria by
epithelial cells of the tonsillar crypts was demonstrated by electron - microscopy.
Inapparent infection was established in three piglets aged six
weeks. The distribution of Stream. suis was essentially similar to
that described above except for an exaggerated presence of Strep. suis
antigen in the majority of the tonsillar germinal centres.
Attempts to identify specific humoral antibody to ;trep. suis
in four older pigs infected systemically with the organism proved
unsuccessful. Similarly immunofluorescent methods failed to
demonstrate specific antibody -containing cells in the tissues of these
four pigs and in the spleens of mice given ,:tree. suis intraperitoneally.