492 



Lymph Nodes, Thymus, and Spleen 



Examination of these curves shows the absolute-weight maximum of the 

 thymus to occur between the ages of 40 to 60 days. This is supported by studies 

 of the thymus weight of some six hundred other animals of various ages in 

 this colony. After the attainment of maximum absolute-weight there is a 



■100 



Ceri/ica/ Lymph Nodes 



/Z5- 



/50 



//s 



200 



22S 



Aae in Days 



Fig. 1. Growth in weight of thymus, spleen, and lymph nodes in male and female rats. 



gradual decline. Studies of the relative-weight curves (not included here) show 

 the maximum relative weight to be attained between the ages of 25 to 45 days. 

 The relative weight is high at birth, rises rapidly, and falls off proportionately 

 as involution of the gland gains momentum. On the basis of these studies, one 

 may consider the thymus as the most labile of the structures studied in that its 

 growth and involution are the most pronounced. The form of the curve ob- 

 tained for the growth of the thymus is similar to that obtained for other 

 colonies, differing chiefly in the time of attainment of maximum absolute- 



