A comparison of the albino rat with man in respect to the growth of the brain and of the spinal cord

In this paper it is proposed to present data illustrating the growth of the brain and spinal cord of the albino rat, and also to compare their growth in this animal with that in man.As a preliminary to this study, it was necessary to determine for the rat the growth curve of the entire body.The observations on this point were published in 1906 under the title " A comparison of the white rat with man in respect to the growth of the entire body" (DONALDSON '06).In that paper it was shown that the growth curve of the rat exhibited all the phases found in the human growth curve, and, further, that the curves for the two sexes were similarly related in both the forms examined.In the present study, therefore, we shall have the advantage of examining the growth of the nervous system in an animal, the general growth curve of which is similar to that of man, and this fact should enhance the significance of the results.The observations to be presented are unique, as the literature contains no extended record of the growth of the brain and of the spinal cord in any mammal below man.Moreover, the observations on man are open to a good many qualifying*criticisms, and it will be most advantageous, therefore, to postpone comment on them until the data from the rat'have been presented.This study of the rat was begun thirteen years ago, and during the interval the records have been accumulating.Throughout this period the rat colony has been composed always of the albino variety of Mus norvegicus (HATAI '07), although occasionally, like weight must be compared, and since the females run to only 255 gms., the numbers available for comparison are somewhat reduced (424 males,218 females).When the data are tabulated, the values given in table 2 show that the weight of the male brain exceeds that of the female in 84 per cent of the groups and is on the average 1.5 per cent greater.TABLE I .Giving the mean observed and calculated weights of the brain and of the spinal cord Brain 680 cases; spinal cord, inthe albino rat.647 cases.Sexes not distinguished. BRAIN WEIGHT (IN GMS.)No. of cases.