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The distribution of cell types in the pituitary gland was studied in a consecutive autopsy series of men over 40 years of age. Among 166 individuals, not previously subjected to prostatic surgery or oestrogen treatment, the proportion of PAS-positive cells was higher in men with hyperplasia or neoplasia of the prostate than among individuals showing a histologically normal prostate. PAS-positive cell counts were negatively influenced by several factors related to wasting disease, while acidophil cells apparently increased in conditions of acute and severe stress. Using multiple regression analysis, benign prostatic hyperplasia was selected as the only one among histological diagnoses which significantly reduced the variability of PAS-positive cell proportion, even when the negative influence of other factors had been accounted for. PAS-positive cell counts did not effectively discriminate between the various forms of abnormal prostatic growth encountered. The data presented indirectly give support to the concept of some form of endocrine derangement in the ageing male.

M. lepraemurium was injected subcutaneously into two inbred strains of mice, C3H and C57/BL, in order to study the local reaction at various time intervals. Within 6 hours an acute inflammatory reaction developed at the site of injection. In the course of the following days it was replaced by a mononuclear infiltrate. The influx of mononuclear cells appeared to be somewhat greater in C57/BL than in C3H mice. Apart from this, little difference was observed between the two strains until at 4 weeks when a vigorous granulomatous reaction developed in the C57/BL strain. This reaction apparently arrested further local spread of the infection. The histological appearance of the inflitrate indicated that a delayed hypersensitivity reaction was taking place. No signs of such reaction was observed in the C3H strain.

Mice with the inbred strains C57/BL and C3H were inoculated subcutaneously on the thorax with M. lepraemurium. In C57/BL mice a firm, raised, sharply defined nodular infiltrate developed 4 weeks afterwards, while in the C3H strain of the infection produced a soft, flattened infiltrate with ill-defined margins, which did not become palpable until 10 weeks after inoculation. A limited spread of the infection occurred early in both strains, but apparently multiplication of the microorganisms was very restricted in C57/BL mice; progressive, disseminated growth of the bacilli was observed in the C3H strain only. In C57/BL mice the granulomatous reaction, developing 4 weeks after inoculation and leading to abcess formation, ulceration and scar formation, apparently inhibited both local multiplication and further spread of the bacilli. In C3H mice no host reaction was detected and the bacilli appeared to grow unrestrictedly. In some C57/BL animals, decrease in host resistance occurred during the infection, causing reactivation of the local lesion and an apparently rapid proliferation of bacilli. Observations regarding the lesions in superinfected animals indicated that a systemic immune reaction develops in the C57/BL strain about 4 weeks after inoculation, whereas this does not occur in the C3H strain.

Mice of the inbred strains C57BL and C3H were inoculated in the foot-pads with Mycobacterium lepraemurium (MLM) and the inflammatory reaction was studied using light and electron microscopy. In C57BL mice a granulomatous reaction developed 3-4 weeks after inoculation. The inflammatory exudate at this stage showed numerous lymphocytes, monocytes and macrophages. The latter cell type often contained many lysosomes and appeared activated. The bacilli which were all within phagosomes showed extensive electron dense aggregates of the cytoplasm suggesting severe damage. Lymphocytes and macrophages in close contact with each other were often observed. In macrophages which contained damaged bacilli, spherical lipid-like bodies surrounded by granular endoplasmic reticulum were observed. It is suggested that this cell product could be of some significance for the bactericidal function of the macrophage. Contrary to these findings, the cellular infiltrate developing in C3H mice showed no lymphocytes and consisted exclusively of macrophages. These were all heavily loaded with bacilli. The vast majority of bacilli encountered in this strain was morphologically intact and presumably viable. Lipid-like bodies similar to those observed in infected C57BL macrophages were not encountered in C3H mice. It is concluded that unless the infected macrophages become immunologically activited they are unable to cause bacterial damage or to inhibit the growth of MLM.