224 GROWTH OF PARTS AND ORGANS 



firmly with strong forceps and then along the entire length of the 

 epididymis this tissue is cut away with sharp scissors, care being 

 taken not to injure the organ itself. A complete isolation of the 

 fat is impossible, but the organ can be so nearly freed that the 

 adhering particles do not modify the results. 



The graph in chart 47 and the values in table 147 were deter- 

 mined by the formulas (30) and (31). (Hatai, '18). 



Weight of thymus on age. In the case of the thymus the data 

 are more useful when presented according to age than when 

 presented according to body weight. 



Technic: In preparing the thymus care must be taken to dis- 

 sect away the large lymph glands as well as the fat lying about it. 

 The records by Jackson ('13) have been combined with those from 

 The Wistar Institute. The graph in chart 48 and the values in 

 table 151 have been determined by the formulas (45) and (46). 

 No weight difference according to sex has been noted. Hatai 

 ('14); Jackson ('13). 



7. Variability. Variation in body weight and organ weight. 

 In table 141 Jackson ('13) gives a series of determinations of the 

 coefficient of variation for body weight on a litter basis and in 

 age groups. The animals were selected by the method of 

 "random sampling." These values are to be compared with 

 those determined by King table 121. 



For the same animals as were used in table 141 Jackson ('13) 

 also gives for the several organs the coefficients of variation 

 (table 142) and the coefficients of correlation with the body weight 

 (table 143). 



8. General tables. The tables which are not represented by 

 charts in the text are usually short and have been introduced 

 where they are mentioned, but as a matter of convenience all 

 of those which are so represented are here grouped together as 

 general tables under the following heads : 



Tables for the increase in the weight of the entire body, brain 

 and spinal cord on age tables 157, and 157 a. 



