The effect of handling rats on their growth and behaviour.

I t has been claimed by a number of workers that handling rats during the early part of their lives makes them grow faster (Weininger, 1954, 1956; Weininger, McClelland & Arima 1954; Ruegamer, Bernstein & Benjamin, 1954; Ruegamer & Silverman, 1956; McClelland, 1956; Levine, 1957; Mogenson, McMurray & Jaques, 1957; Levine & Otis, 1958), though others have not invariably obtained this result (Scott, 1955; Mogenson & Ehrlich, 1958). The term ‘handling’ in this connexion has implied gentle treatment. In most instances it has involved stroking the animals; some American authors have preferred to use the word ‘gentling’. Levine (1957), however, pointed out that simply moving the animal from the nest for a period of 3 min had the same effect. If it is true that this ‘gentling’ in some way increases the growth rate, the situation has human implications, for it is well known that extra ‘tender loving care’ may be all that is needed to make babies thrive when they are parted from their mothers and live in institutions and hospitals. Part of this ‘tender loving care’ undoubtedly involves taking more time and trouble over feeding, and consumption of more food may be why some of these babies grow faster. On the other hand, a psychological reason may predominate, for Widdowson (1951) found that schoolchildren living in an orphanage in Germany gained weight and height less rapidly when they were anxious and unhappy than when they were not and grew less rapidly than children of similar age distribution in another orphanage where the atmosphere was congenial and happy, although the unhappy children in fact ate more food. The analogy with children, however, cannot be drawn too closely. Some workers have suggested that the effect on the young animal is one of disturbance and mild stress, caused perhaps by its removal from the warm nest. Further, handling of animals by man involves two species, and it may well be that stimulation of some sensory organ, for example the olfactory one, is as important as the tactile stimulation of the skin. The object of our experiments was to try to confirm and at the same time to explain the observations of Levine and others. Three experiments have been made. In the first, male rats were handled daily from weaning at 3 weeks till they were 9 weeks old, and their growth and behaviour were compared with those of unhandled litter-mates. In the second and third, all the members of some litters were handled daily during the suckling period and their progress was compared with that of the young in other undisturbed litters. * Present address : Department of Psychology, University of Aberdeen.