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A new method has been developed for observing single, or small groups, of cells at an angle that can be varied from 0 to 360°. A better understanding can thus be achieved of cell/cell and cell/substrate interactions during locomotion, adhesion and, especially, emperipolesis and phagocytosis.

A new way of illuminating and photographing cells in profile has been developed, showing at the same time their images reflected in a glass substrate. Through its use in cinemicrography, the kinematics of cells and their adhesions can be observed with certainty, thus permitting a better understanding of their mode of locomotion.

1. The optimum conditions for vaccinia virus multiplication in shavings of adult rabbit skin maintained in rocker flasks in a fluid medium have been investigated. Satisfactory virus multiplication occurred in 5 ml. of medium containing 40 per cent, rabbit serum, 40 per cent, phosphate-buffered saline, and 20 per cent, mouse embryo extract; an air atmosphere was used. 2. A growth curve for vaccinia virus grown in vitro under these conditions was obtained by estimating the virus content of cultured skin at known intervals after inoculation. The curve was essentially similar to that obtained by growth of vaccinia in vivo, and could be divided into three phases: (a) during the first few hours infectivity fell, (b) from 10 to 40 hours there was a rapid increase of infectivity, and (c) flattening of the curve started after 40 hours, although some increase of virus continued, until, at 80 hours, the concentration of virus present was at a maximum. 3. An attempt is made to correlate the multiplication of virus with the cytological changes known to occur in infected cells.

Stretches of regenerating rabbit’s nerve in which no connexion with the periphery is allowed contain numerous and small nerve fibres. Both cutaneous sensory and motor nerve fibres become large when allowed to reach their endorgans, but the motor fibres attain greater diameters than the cutaneous sensory fibres. Motor fibres regenerating without opportunity of reaching muscle fibres become little if any larger than sensory fibres when both are unable to reach their end-organs. It is, therefore, probable that the peripheral connexion is of great importance in determining fibre diameter. The fibres of the central stump of a nerve regenerating unconnected with the periphery remain small and have relatively very thick myelin sheaths. The diameter of nerve fibres regenerated in the region below a crushed point on a nerve is not influenced by the length of nerve to be regenerated distally. Increase of diameter and medullation proceeds centrifugally from a lesion, more distant points showing a lesser degree of maturation at any given time. Fibres regenerated in a grafted piece of posterior tibial nerve were only slightly smaller than those in a grafted piece of peroneal nerve. Connexion with the periphery is, therefore, able to produce an increase in fibre diameter which overrides any constriction of fibre growth produced by the slightly smaller Schwann tubes.

The goldfish (Carassius auratus) learns to swim to concealed food when an illuminated disk is presented. The presentation of an olfactory stimulus at the same time as the optic stimulus, during reinforcement of this visual learning, results in the addition of the olfactory stimulus to the stimulus complex necessary to call forth the learned reaction. Five animals learned to react to a situation in which—after preliminary training with an optic stimulus with food as reward—amyl acetate was given as olfactory stimulus and the optic stimulus as reward. This effect is termed second-order learning. It is comparable to second-order conditioned reflexes. In four animals trained in this way operations involving removal of large areas of the optic tectum, or cuts made at its anterior border, caused disturbances in the second-order learning. There exists, therefore, in the Teleostean optic tectum a mechanism capable of second-order olfactory-optic learning. The connexion between the telencephalic primary olfactory centre and the tectum involved in this learning passes into the tectum at its anterior border, since cuts made in this region interfered with the learning while leaving a great deal of the tectum intact.

Animal tissues contain two types of nucleic acid: the desoxypθntose, or thymo-, nucleic acids whose distributionis confined to the nucleus; and the pentose, or yeast, nucleic acids which can occur in both nucleus and cytoplasm. For many years.it has been possible to identify desoxypentose nucleic acid by means of the Feulgen reaction, although, as has been frequently pointed out (Lison, 1936; Stowell, 1943), this must be carried out under carefully standardized and controlled conditions if its results are to be reliable. No corresponding test for pentose nucleic acids existed until Brachet (1940, 1941) showed that it was possible to identify pentose nucleic acids by comparing sections stained with basic dyes with other sections similarly stained following treatment with a pancreatic extract containing the enzyme ribonuclease. Therefore a distinction between the two types of nucleic acid may be made by applying both the Feulgen and Brachet tests to the same material. However, since the stains used in the two cases are different, and one set of sections is subjected to acid hydrolysis and the other is not, it may be difficult to relate the two cytological appearances to one another.