34 C. M. JACKSON 



They therefore agree fairly well with the curve from Hatai's 

 formula. The data are too few for calculation of the coefficients 

 of variation and correlation at the various ages. 



A complete series of observations is available for the stomach 

 and intestines plus contents, however, a summary of which is 

 given in table 12 and figure 5. The increase in relative weight 

 runs somewhat parallel to that for the empty tract, increasing 

 from an average of about 6 per cent of the body weight in 

 the newborn to a maximum of about 16 per cent at six weeks, 

 decreasing thereafter to about 7 per cent at one year. 



The coefficient of variation for the canal ivith contents (calcu- 

 lated only to six weeks) is somewhat high, 28.6 to 42.1, but not 

 so high as was anticipated. It is, as might be expected, highest 

 in the newborn (only a part of which had suckled) and at twenty 

 days (weaning period). The coefficient of correlation between 

 body weight and canal with contents is low in the newborn (0.29) 

 but comparatively high later (0.59 to 0.84), partly due to 'spuri- 

 ous correlation.' Although one naturally thinks of the alimentary 

 canal with contents as exceedingly variable in size, it is inter- 

 esting to note that it is actually less variable than some other 

 viscera. In general, after the newborn age, it is usually less 

 variable and more closely correlated with the body weight than 

 are the ovaries, spleen and suprarenals. It is on account of this 

 degree of correlation between body weight and alimentary canal 

 with contents that in the rat the gross weight serves almost as 

 well as the net body weight as a basis for estimating the relative 

 weight of the various organs. 



1 1 . Suprarenal glands 



From the curves of relative (percentage) weight (fig. 4) cal- 

 culated according to Hatai's formulas, it is seen that the relative 

 weight of the suprarenals in the male increases from 0.031 per 

 cent of the body at 5 grams to a maximum of about 0.040 per 

 cent at 10 to 15 grams, thereafter decreasing to 0.038 per cent at 

 20 grams, 0.030 per cent at 50 grams, 0.021 per cent at 120 grams, 

 0.018 per cent at 160 grams, and 0.014 per cent at 300 grams. In 



