212 



GROWTH OF PARTS AND ORGANS 



The weight of the spleen on the body weight. Technic: The 

 vessels were cut close to the hilum. The determination of the 

 weight of the spleen is complicated by the occurrence of '^en- 

 larged spleens"^ — so called. These differ from the normal by 

 being often several times the normal weight, darker in color, 

 soft to the touch and showing on the surface dark or grayish 

 patches. Spleens with these characters plainly marked were not 

 used. The graph in chart 35 and the values in table 145 were 

 determined by formula (19). No sex difference was observed but 



r Chart 35 Showing the weight of spleen of the male albino rat according to 

 body weight. The observed weights are represented by 87 male rats. Table 

 145, formula (19). 



Observed weight. 



Calculated weight. 



the graph is based on male records only. Hatai ('13); Jackson 

 ('13). 



The weight of both lungs on the body weight. Technic: The 

 lungs are severed from the trachea and the portion of the esoph- 

 agus usually taken out with them is removed. After the first 

 three months of life the lungs of the rat are often infected. Such 

 iufected lungs may be highly altered — but are always abnormally 

 heavy. The endeavor has been made to exclude infected lungs 

 from the series — but doubtless some have been used. The 



