much less than do mechanical stimuli. The reaction usually involves an immediate quickening of rate, varying with the color of the light, and occasionally diminutions of amplitude and minor irregularities of contour. 4. Since an agreement was found between the color preferences and the increase in breathing rate caused by colored light, it would seem that agreeable feelings are accompanied by respiratory quickening (and perhaps by shallowing and irregularity). 5. Daily reactions of four birds to three intensities of light, one intensity per day, showed no direct relation between amount of stimulus and amount of reaction. The second daily reaction showed the influence of repetition, since considerably weaker than the first; but thereafter was seen a continuous increase in amount of response. 6. Meaningless stimuli, as pistol shots, quickly lose their disturbing influence upon respiration, although it remains sensitive to those of a significant character, such as noises made by other birds. A stimulus which no longer influences the breathing, will sometimes occasion disturbance if accompanied by a second stimulus, of another order, even though of weak intensity. THE EFFECT OF THE BEARING OF YOUNG UPON THE BODY-WEIGHT AND THE WEIGHT OF THE By JOHN B. WATSON. (From the Neurological Laboratory of the University of Chicago.) With Plate VI. By observations in this laboratory the results of which are as yet unpublished', the normal increase in the body weight of the female white rat, uninfluenced by the bearing of young, has been determined. In this connection, a question arose as to the effect on the body growth, if the females were allowed to breed normally. The present paper reports the results of an investigation carried out in answer to this question. In addition to the above, there arose the further question, as to the effect of the bearing of young upon the weight of the central nervous system, and on the percentage of water contained in it. So far as the writer knows, only three men have published observations bearing directly upon the subject in hand; viz., EDLEFSEN, HENSEN and MINOT. Un EDLEFSEN recorded the changes in the weight of 7 female guinea pigs from birth to the end of their first pregnancy. fortunately he compared the weight of the females during preg nancy with the weight of the males of a corresponding age. He made two points clear: Ist, the actual growth of the female guinea pig is slower during the period of gestation than that of the males of the same age during the same time; 2nd, that while the true body weight of the mother immediately after parturition is less than that of the male of corresponding age, 'It is expected that the results of this investigation will be published at an early date. still if we consider the weight of the mated females just at the end of the period of gestation (before partuition), or better if we add the weight of the young, immediately after birth to that of the mother, we shall find that the weight of the breeding female is in the ratio of 1. 164:1 to that of the male. The relationship after parturition (not adding the weight of the young to that of the mother) is 0.848: 1. HENSEN in an Anhang to EDLEFSEN's work, made some observations upon a litter of 4 guinea pigs, 3 females and I male, in order to determine the relationships between the growth of unmated females and males and thus supplement the results of EDLEFSEN. To control his results he mated one of the females. The following table presents his conclusions: The weight of the mother just before parturition was 612 grammes. In this table we find some slight ground for inferring that the males grow at least as rapidly as the unmated females. On the other hand, the figures point to the fact that breeding females, reckoning in the weight of their young, actually build up more bodily material, than either the unmated females or males during a corresponding period of growth. HENSEN then tried to determine the total increase in weight of one mated female during the period of gestation, apart from the increase in weight of her young. He began his reckoning at the time pregnancy first became noticeable. This happened on the 28th day after conception. The female weighed 335 gr. at this age. In the remaining 39 days of pregnancy (28 + 39 days period of gestation) she herself gained 100 gr. in weight and produced 146 gr. of bodily substances in young and adnexa, i.e. 1.46 times more than she herself gained. MINOT tabulated the average changes in the weights of 66 female guinea pigs, from the beginning of the period of gesta tion to parturition, and then again for 35 days immediately after parturition. The usual length of the period of gestation is from 67 to 68 days. The average weight of the 66 pregnant guinea pigs just before delivery was 830.2 gr. Their average weight 3 days after delivery was 588 gr. The average weight of unmated females at that age, he had previously determined from many observations to be 532.1 gr. Thus it appears that at the end of pregnancy, the breeding females were heavier than those not allowed to breed, by about 55.9 gr. MINOT'S tables presenting the average alterations of weight of these 66 guinea pigs. from the 35 days immediately after the delivery of their young, show that there is a very great loss of weight, especially marked during the earlier days of this period. Subsequently there is a slower loss in weight continuing for about three weeks, after which recovery begins. Owing to the destruction of MINOT's pigs-the story of which has become classic in the annals of American researchfurther investigation of this subject was cut short. If we compare the results of EDLEFSEN and HENSEN'S observations on the growth of gestating guinea pigs during their first pregnancy, with those of MINOT, we find a contradiction. EDLEFSEN and HENSEN conclude that the growth of the gestating females, when considered apart from the young developing in them, is slower than that of either the unmated females or males. MINOT, on the contrary, concludes that the mated females immediately after partuition are heavier than the corresponding unmated females by 55.9 gr. On account of the large number of animals with which MINOT worked, his results are probably the more reliable. Observations upon the Body-weight of the White Rat. The writer's observations were begun upon a series of rats in the spring of 1903 and were continued for approximately one year. The females under observation were selected from five litters of rats born in April and May of that year. The rats in these litters were of good stock, strong, healthy, and large for their age. In the following description of results, these five groups are referred to under the letters A, B, C, D, and E. At the beginning of the experiments Each of the above-named groups, at 70 days of age (the age at which sexual maturity is reached), was divided into approximately equal sub-groups, one containing the rats which were to be mated, the other, those which were to remain unmated. Since we desired to make the condition for growth as nearly ideal as possible, we fed the rats used in this experiment very carefully, giving them always a rich and varied diet. Baker's bread, softened with unskimmed milk, was the chief article of food. Since food of this character is likely to sour if left in the cages, only so much of it was given as could be consumed by the rats from one period of feeding to the next. Sunflower seed and cracked corn were always kept in the cages. Vegetables and meat were given once a week. Great care was taken to avoid surfeiting the rats. They were fed each morning between nine and ten o'clock. The rats were weighed once a week, and weighing came always before feeding. The experiment was conducted in a warm, sunny room, the temperature of which was kept constantly above 70° Fahrenheit. At 70 days of age1 the rats destined to bear young were 1At this age the average weight of the unmated rats approximately equalled that of the mated. A slight difference, however, existed in favor of the mated rats (2 gr. heavier on the average). |