STUDIES OF THE GROWTH IN ICR-JCL MICE

I. BIOMETRIC STUDY OF PROPORTIONAL PHYSICAL GROWTH

Abstract

One hundred and fifty-five off springs of ICR-JCL mice, composed of 74 females and 84 males from 8 fathers and 16 mothers were subjected to study the growth of various parts of the body from the 3 rd to the 71st day after birth.
About 10 mice each, picked up at random from total members of sixteen litters were grouped at weekly interval corresponding to growth. The animals were killed by ether and placed ventrally on a board. The lengths of head, trunk, and tail, as well as body weight were measured. This procedure was repeated three times, ranged over a year and aimed at elimination of possible influence of different season of the year to growth. The mean value and standard deviation of each stage of growth were calculated.
Using the average values of the different parts of the body obtained, the absolute growth of each part and the relative growth between two different parts of the body were studied. The results were summarized as follows.:
1) The length of the head reached its maximum within 6 to 7 weeks after birth, presenting the most rapid growth among the subjected parts. Such growth of the head might be of neural type, in contrast to the other subjected parts showing lymphoid type of growth.
2) The increase of tail length was far more prominent when compared with that of the trunk or head. Although the tail was shorter than the trunk one week after birth, the rate of the tail to the trunk increased rapidly during the second week. Near the complete maturation at 9 to 10 weeks after birth, the lengths were approximately 1.5, 2.5 and 5 times respectively in the head, trunk and tail, as compared with that of each parts at one week after birth.
3) From the change of external appearance of various parts of the body, the developmental stage in mice was presumed to be divided into two periods, the first covering 3 weeks after birth and the second from 4 to 7 weeks. The maturation in outward appearance was completed at the 7 th week of life, whereas the body weight reached its maximum 8 to 9 weeks after birth.