CHANGES IN COMPOSITION OF BODY OF RAT 



27 



3. The groivth of dry substance 



In order to determine the amount of moisture in the body, the 

 rats (after two weeks of age) were minced in the meat grinder. 

 During the process of grinding a slight amount of blood and 

 tissue is lost. However this loss is negligible in comparison 

 with the entire body weight. Some water is also lost from 

 evaporation, though it may be very slight, but as we are esti- 

 mating the moisture in terms of the intact body weight, such 

 loss will not disturb the results. The bodies of the smaller 

 rats were dried directly after several incisions had been made 

 on the body, as well as an opening into the skull. The bodies 

 were dried in the oven at a temperature of 95° to 98°C. for 

 one week. One week at such a temperature is more than suf- 

 ficient to bring the material to a constant weight. 



The weight of the dry substance during the first six weeks of 

 life, together with that at 294 days, is given in table 4, and its 

 graphic representation in chart 1. 



TABLE 4 



Showing the growth of dry substance during the life span of the albino rat 



Number of rats. . . 



Body grams 



Water, percentage 



Solids, grams 



Solids, percentage 



AGE IN DAYS 



Birth 



43 

 4.3 



87.2 



0.6 



12.8 



10.2 



79.8 



2.1 



20.2 



15 



9 



13.5 



72.9 



3.7 



27.1 



b 



24.9 



70.6 



7.3 



29.4 



28 



3 

 47.3 

 69.6 

 14.4 

 30.4 



35 



3 

 52.5 

 70.6 

 15.5 

 29.4 



42 



3 

 65.8 

 69.4 

 20.1 

 30.6 



294 



277.5 

 65.3 

 96.4 

 34.7 



Chart 1 shows that the drj^ substance increases very rapidly, 

 especially during the first two weeks of life. At the end of the 

 third week the proportional amount of solids in the entire body 

 (30 per cent) reaches almost the maximum (35 per cent). Thus 

 after the end of the third week the increase is small compared 

 with the increase which took place during the first three weeks, 

 and indeed at the end of one year its increase is only slightly 

 over 5 per cent more than that at the end of the third week. 



This rapid increase of the dry substance is extremely interest- 

 ing in view of the high value reached while the young are 



