The present experiment was planned as ah attempt to obtain conditioning of an emotional response in monkeys when the usual sequence of stimuli was reversed (i.e., backward conditioning).Backward conditioning is extremely important from a theoretical standpoint, as is evident from the part it plays in the learning theories of Hull (6), Hunter (7), and Guthrie (4).The contradictory nature of experimental data concerning backward conditioning has been pointed out by Cason (3). Two typical conditioning experiments, one carried out by Wolfle ( 12), and another by Switzer (11), have been widely quoted as evidence for backward conditioning. In both experiments the conditioning was of a skeletal muscle response in human subjects. In such a situation conditioning can be influenced by verbal activities [see Cason (2)].By the use of animal subjects, such as monkeys, the effects of verbalization can be avoided. The data of Pavlov (8) and Yarbrough (13) on animal learning suggest that backward conditioning may be impossible in sub-human animals.

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Experiments by Spence (1934) on chimpanzees and Johnson (1914) on a cebus monkey have demonstrated these primates to have minimum separable visual acuity which compares favorably with that of man. On the other hand, visual acuity has been found to be significantly inferior to that of man in dogs (Johnson, 1914), cats (Smith, 1936), rats (Lashley, 1930), chickens (Johnson, 1914), and pigeons (Hamilton andGoldstein, 1933; Chard, 1939). 3 In order to discover the status of rhesus monkeys with regard to this visual function, measurements of minimum separable acuity were made for two of these animals and two human subjects in the present study.

97 USAF pilots and 79 college men read 12 settings each on 9 experimental altitude indicators to evaluate speed and accuracy of quantitative readings. Results indicate that (1) instruments that combine the indications from two or more pointers or rotating subdials are conducive to large reading errors; (2) indicators on which the digits are already combined in the proper sequence are more easily read; (3) speed and accuracy of instrument reading are positively correlated; (4) college men and USAF pilots showed virtually the same pattern of results.

FIVE FIGURES INTRODUCTORY STATEMENTThe chimpanzee breeding colony of Yale Laboratories of PFimate Biology, maintained at Orange Park, Florida, offers increasingly favorable opportunity for such long-continuing studies as that of weight-growth. This report is a sequel to the publications of Bingham ('29) and Spence and Yerkes ('37). It includes and is based largely upon additional data. For the first time it is possible to offer provisional weight iiorms for the full-grown adult male and female chimpanzee in supplementation of our tentative growth norms. That these standards for the colony-reared ape will apply without correction to the species in the wild seems doubtful. On the whole, conditions of life and growth are much more stable and favorable in the laboratory colony than in nature.Because of the unsatisfactory status of the classification of the genus Pan, we have made no attempt to classify our data by species. Almost certainly two or three varieties, races, or species are represented. We seriously doubt that there is more than one true species.The chimpanzee population of the laboratories numbered forty-six on June 1, 1940. Heretofore weight at birth and Measurement of chimpanzee body weight during the 15-pear period of observation which is covered by this report has been the work of many hands, and our obligations therefore are numerous. We reaffirm the general acknowledgment made by Spenee and Yerkes ( '37, p. ?29), and express appreciation of the services of Superintendent W. C. Atwater and his helpers, who have carried major responsibility for the heavy task of transfer of our animals to the scales.