GROWTH OF THE SKELETON 241 



In table 68 of 'The Rat' (Donaldson, '15) a series of normal 

 body weights for each millimeter of body length is given for each 

 sex. When the observed body weight of a rat fell 5 per cent or 

 more below the table value given for the observed body length, 

 the observed value was corrected to the table value, on the as- 

 sumption that some unfavorable nutritional condition had reduced 

 the body weight temporarily. 



On the other hand, we had in the case of many of the old rats 

 a record of their maximum body weights, reached earlier, and 

 often well above those observed at the time of killing, and also 

 above the table values, and in such instances the maximum body 

 weight was that entered in the table. These two procedures 

 eliminated from the table subnormal body-weight values. 



To prevent a misuse or misinterpretation of the values given 

 in the tables which follow, we repeat that the absolute weights 

 given are those found after maceration in the 'Gold Dust' wash- 

 ing powder (Appendix 2) . 



This treatment reduces the weight of the bones in all cases, 

 but especially in those rats less than 100 grains in body weight or 

 70 days of age. The percentage of water is also reduced somewhat. 

 The lengths of the bones are but very slightly affected. The 

 effects of the maceration are, however, sufficiently similar among 

 the different bones to make determinations of relative values 

 based on the macerated bones applicable to the perfectly fresh 

 bones also. 



The most evident need for the corrected values is in comparison 

 between the body weight and that of the skeleton or some of its 

 parts — since in these instances the true weights are needed to 

 give the correct ratios— and when such ratios are desired the 

 proper corrections must be made. 



It should be added, however, that though the relative values of 

 the skeleton and its parts, as shown in table 2 and chart 2, are 

 somewhat modified by the use of the corrected data, yet the 

 modification is slight and, moreover, does not affect the interpre- 

 tation given to these records. 



The values in our tables may be used therefore as standards 

 for comparison with determinations from other rats, the bones 

 of which have been macerated by the same or a similar process. 



