42 C. M. JACKSON 



balanced by a corresponding increase in the musculature, which 

 by its large size virtually dominates the further growth of the 

 body as a whole. 



It is further evident that the growth of tiie body as a whole 

 is the resultant of unlike growths of its various component sys- 

 tems. This principle applies likewise to the growth of the vis- 

 ceral group, the various organs having each its own characteristic 

 mode of growth. As a matter of fact, only three individual 

 organs, thymus, heart, and kidneys (and perhaps also the supra- 

 renals) have their apparent maximum relative weight at the age 

 of three weeks, when the visceral group as a whole appears rela- 

 tively largest. The stomach and intestines and the liver appar- 

 ently reach their maximum relative weight at the latter period 

 of six weeks, and the gonads at ten weeks. Of those reaching 

 their maximum at an earlier period, the brain, spinal cord, eye- 

 balls, lungs, and spleen appear to be relatively heaviest in the 

 second week while the thyroid gland appears relatively heaviest 

 in the newborn. 



Somewhat similar relations as to the relative growth of the 

 various organs were found by Kellicott ('08) in the dogfish. Of 

 the various organs observed, only the brain and rectal gland 

 appear relatively largest at birth. The heart, pancreas, spleen 

 and liver increase rapidly so as to reach their maximum relative 

 size a short time after birth, and thereafter decline steadily (with 

 a secondary increase in the liver, due to accumulation of fat). 

 The gonads reach their maximum relative size at sexual maturity 

 in the dog-fish. 



Scattering data for the growth of the human viscera are re- 

 corded by various authors (for references, see paper by Jackson 

 '09), but they are scarcely adequate to determine the question 

 as to the course of postnatal relative growth for the individual 

 organs. In general, so far as may be judged from the data avail- 

 able, the human visceral group appears relatively larger at birth 

 than at any subsequent age. The lungs, however, appear to 

 increase somewhat in relative weight so as to reach a maximum 

 after birth. This is perhaps also true of the heart, kidneys and 

 gonads, and it is quite possible that more extensive data would 



