William O, Reinhardt ^g^ 



weight. This may be related to colony differences, environmental conditions, 

 or differences in the onset of puberty. 



Figure i also presents the curves for the growth in absolute weight of the 

 spleen. No correction has been made in the means for the variation in weight 

 of the spleen which occurs within the groups and which is evidenced by the 

 large standard errors. It is realized that weight studies of the spleen must take 

 into account the relation between the blood and lymphoid elements of that 

 organ. An attempt was made to standardize the technique of autopsy and dis- 

 section in order to render this relationship as nearly constant as possible, 

 although other factors may complicate this problem. The average values for 

 the weight of the spleen are greater for the male than for the female after the 

 age of 50 days. There is a gradual leveling off in the absolute weight of the 

 spleen in each sex, but studies of the relative weights show that there is a com- 

 parable decline for each sex after 100 days of age. The reason for the greater 

 absolute weight of the spleen in the male is not apparent. Donaldson^ states 

 that there was no apparent difference between male and female spleen Aveights 

 in material employed by him in his studies. 



The form of the growth curve for the cervical lymph nodes is similar in 

 males and females. There is an increase in weight to the age of 100 days and 

 then a gradual decline, but not as marked as in the case of the thymus. A study 

 of relative-weight curves shows the same phenomenon as is the case for the 

 absolute weights. One may speak of growth and involution in weight of the 

 cervical lymph nodes on the basis of these curves. The form of growth curves 

 for the cervical lymph nodes is generally similar to those of Hellman* for the 

 rabbit, and those of Chiodi* for the rat. These investigators employed the 

 same technique as here utilized, but they have examined other groups of 

 nodes in smaller numbers of animals. 



Growth of the mesenteric lymph nodes in absolute values is the same for 

 males and females. Maximum weights in both sexes are attained at about the 

 age of 60 days, after which time the weights remain fairly constant. Relative 

 to body weight, the weights of the mesenteric lymph nodes show a slow decline 

 (after the age of 40 days). Since the absolute weights of the mesenteric nodes 

 remain constant for the various age periods after the age of 60 days, there is 

 relatively more mesenteric node tissue in the female because the latter does 

 not attain the same body weight as the male. This contrasts with the case of 

 the cervical lymph nodes in which the form of the absolute- and relative-weight 

 curves for male and female are more nearly the same. Since the mesenteric 

 nodes apparently have a different function from that of the cervical nodes, 

 particularly in relation to the absorption of food from the intestine, it is pos- 

 sible that the growth and maintenance of the former may depend on other 

 factors, such as food absorption. 



Aside from interest in a comparison of the growth curves of the thymus, 

 spleen, and lymph nodes, the value of these studies lies in their application to 

 experiments devoted to elucidation of the function of these structures in the 



