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Integrating microdensitometry was used to study changes in the intracellular activity of 4 enzymes during macrophage development. Suspension cultures of blood monocytes from 19 healthy human subjects were examined at 0, 2, 4 and 6 d. Mononuclear phagocytes were harvested by glass adherence and standard methods were used for cytochemical staining for NADH dehydrogenase, succinate dehydrogenase, acid phosphatase and alpha-naphthyl butyrate esterase. All specimens from all subjects were stained at the same time and staining intensities in individual cells were measured at appropriate wavelengths. A highly significant increase in enzyme activity with culture time was found for all 4 enzymes. These increases in mitochondrial, lysosomal and ectoenzyme activities during development indicate the increasing functional capabilities of the macrophages.

The development of macrophages from the blood monocytes of ten normal subjects has been studied at intervals over a six day period. Suspension cultures were used to obtain randomly orientated cells and morphometric measurements were made on electron micrographs. In order to meet the requirements for normality of distribution and homoscedasticity, data were logarithmically transformed. A two-way analysis of variance was then carried out, taking subjects and time intervals as fixed effects, and using a least significant difference procedure to detect variations between culture time intervals. The whole cell and cytoplasmic volumes showed 3-4 fold increases during culture. The cell surface area more than doubled; this was partly attributable to the larger cell volume and partly to increased surface irregularity. The mitochondrial volume also showed a similar significant increase, attributable to an increase in both number and size of mitochondrial profiles, the cytoplasmic volume fraction remaining approximately constant. Although there was a statistically significant increase in nuclear surface area, the nuclear changes were relatively small. The results and the application of appropriate statistical methods have thus provided basic morphometric data for human macrophage development in culture. The experimental system should permit further investigation of factors governing impaired macrophage development in malignant disease.

Hypertrophy of the extensor digitorum longus muscle after surgical removal of its companion tibialis anterior muscle has been studied in mice. Early, intermediate and late stages in the process of hypertrophy have been defined. The proportional increase in the man cross sectional area of fibres in a hypertrophic muscle consistently exceeded the proportional increase in the weight of the same muscle in all animals. This suggests that hypoplasis (loss of fibres) was occurring. This work was carried out with the aid of grants from the Medical Research Council and Science Research Council of Great Britain.

The sizes of the different types of muscle fibre in the extensor digitorum longus (EDL) muscles of mice have been measured, EDL muscles showing compensatory hypertrophy following the removal of the tibialis anterior muscle 116 days previously being compared with normal contralateral controls. Contrary to previous findings, the hypertrophy was well maintained after 116 days and Type II fibres were enlarged preferentially.