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This basic text is the first modern work of its kind to develop an integrated and consistent approach to the science of psychology as a systematic, interpretative account of social behavior. A large part of the book is devoted to the basic principles of human behavior, which are then "spelled out" in their operation in such behavior as racial prejudice, labor-management conflict, propaganda, group morale, leadership, international tensions, etc.

In a recent paper we summarized reasons for predicting that increasing an animal's experience should lead to a rise in activity of the enzyme cholinesterase (ChE) in the brain. We reported there that the brains of rats exposed to the condition of environmental complexity and training (ECT) did differ from those of littermates kept as isolated controls (1C), but the differences were not entirely as predicted: in the cerebral cortex, the ECT animals had significantly less ChE activity per unit of weight of tissue; in the rest of the brain, the ECT animals had significantly more ChE activity per unit of weight. We also indicated that a study was then in progress to attempt to specify more precisely the loci of these enzymic changes-both in the cerebral cortex and in the rest of the brain. In the present paper we report first on a replication of the original experiment; secondly, on new findings that help explain why ChE activity of ECT animals decreased in the cortex while increasing in the rest of the brain, and thirdly, on attempts to specify further the sites of enzymic changes. METHODS SubjectsOur previous experiment used 75 littermate pairs, 150 animals from six different strains, one rat of each

We have previously reported anatomical and chemical changes in the cerebral cortex of rats living in an enriched, stimulating environment. The present study includes additional histological measures such as more extensive depth measures, differential cell counts, and cell size measurements.Celloidin-embedded, thionin-stained sections of the visual cortex from environmentally enriched rats and their impoverished littermates were measured. Two methods for calculating cortical depths were used: one, with an ocular micrometer taking eight measures lateral to the elevation in the corpus callosum on each hemisphere; two, on enlarged photographs taking 51 measurements 2 mm apart on each hemisphere. With the ocular micrometer method the cortical depth of the enriched brains was 6.4% greater than the depth of the impoverished cortex. O n the enlarged photographs the more medial depths in the enriched rats showed greater increases than the lateral depths.Overlapping photomicrographs were made of a medial cortical area 1.00 mm by 0.75 m m on each transverse section and were combined into one composite picture for each animal. Differential cell counts from the composite pictures were determined independently by two technicians. Results indicate a 14% ( p < 0.01) increase in glia among the enriched rats, No significant differences between enriched and impoverished groups were found in the perikarya and nuclear circumferences as measured with a planimeter from camera lucida drawings.We have previously reported that an enriched behavioral environment brings about measurable morphological changes in the rat brain (Diamond, Krech and Rosenzweig, '64; Bennett, Diamond, Krech and Rosenzweig, '64). In those experiments, depths and differential cell counts were taken on frozen, thionin-stained sections from the brains of rats living for 80 days in enriched or impoverished conditions. From these sections we found a 6.2% increase in the depth of the visual cortex of the rats from the enriched environment. The same sections were used for differential cell counts of the neurons and glia cells. The cells were counted in a series of microscopic fields proceeding from the pial surface of the cortex down to the underlying white matter. By this method, the number of neurons per field was about 17% fewer in the enriched rats while the number of glial cells per field was about 7% less; in other words, the J. COMP. NEUR., 128: 117-126.glial/neural ratio was 12% higher in the enriched rats than in the impoverished rats; a difference in this direction was found in 14 out of 18 pairs compared. All measurements and counts were done "blindly," i.e., the anatomist did not know whether she was working with a section from an enriched or an impoverished rat.The present study (experiments I11 and IV) can be seen as a replication and extension of the previous study to be referred to as experiments I and I1 (Diamond, Krech and Rosenzweig, '64). The new study includes more critical histological measures such as classifying types of glia and determini...

relative mobilities and the numbers of the different carriers. 7. The usual test of the quality of a crystal is its residual resistance ratio, that is, the ratio of the resistivity at room temperature to the resistivity at 4.2?K. Although at present there is no way to relate the resistance ratio and purity of one metal to the resistance ratio and purity of another, the ratio is a reliable test between different samples of the same metal. The resistance ratios of the best samples currently available of some of the metals discussed here are, Cu, 8000; Zn, 60,000; Sn, 100,000; Fe, 300; Ni, 2700; Mo, 4000; W, 80,000. 8. Yu. Gaidukov, Soy. Phys. JETP (English Transl.) 10, 913 (1960); J. R. Klauder and relative mobilities and the numbers of the different carriers. 7. The usual test of the quality of a crystal is its residual resistance ratio, that is, the ratio of the resistivity at room temperature to the resistivity at 4.2?K. Although at present there is no way to relate the resistance ratio and purity of one metal to the resistance ratio and purity of another, the ratio is a reliable test between different samples of the same metal. The resistance ratios of the best samples currently available of some of the metals discussed here are, Cu, 8000; Zn, 60,000; Sn, 100,000; Fe, 300; Ni, 2700; Mo, 4000; W, 80,000. 8. Yu. Gaidukov, Soy. Phys. JETP (English Transl.) 10, 913 (1960); J. R. Klauder and J. E. Kunzler, The Fermi Surface, W. A. Harrison and M. B. Webb, Eds. (Wiley, New York, 1960), p. 125. 9. A. B. Pippard, Phil. Trans. Roy. Soc. London A250, 325 (1957). 10. A description of these experimental techniques for determining the shape of the Fermi surface is given by A. B. Pippard, Rept. Progr. Phys. 23, 176 (1960); their application to copper is given in several papers in The Fermi Surface, W. A. Harrison and M. B. Webb, Eds. (Wiley, New York, 1960). 11. For studies of tin, see N. E. Alekeseevskii, Yu. P. Gaidukov, I. M. Lifshitz, V. G. Peschanskii, Sov. Phys. JETP (English Transl.) 12, 837 (1961); for studies of lead, see N. E. J. E. Kunzler, The Fermi Surface, W. A. Harrison and M. B. Webb, Eds. (Wiley, New York, 1960), p. 125. 9. A. B. Pippard, Phil. Trans. Roy. Soc. London A250, 325 (1957). 10. A description of these experimental techniques for determining the shape of the Fermi surface is given by A. B. Pippard, Rept. Progr. Phys. 23, 176 (1960); their application to copper is given in several papers in The Fermi Surface, W. A. Harrison and M. B. Webb, Eds. (Wiley, New York, 1960). 11. For studies of tin, see N. E. Alekeseevskii, Yu. P. Gaidukov, I. M. Lifshitz, V. G. Peschanskii, Sov. Phys. JETP (English Transl.) 12, 837 (1961); for studies of lead, see N. E.