206 GROWTH OF PARTS AND ORGANS 



(a) Body weight per millimeter of body length. The relation 

 between body weight and body length is shown by dividing the 

 weight by the length and thus getting the weight per running 

 millimeter — table 122. 



These determinations show that after the middle of the suckling 

 period, at about nine days of age, the values for the female 

 exceed those for the male, and this excess tends to increase as 

 the body length increases. 



4. Organs with an early rapid growth. Brain weight on body 

 weight. Technic: The rat was first eviscerated — ^this leaves in 

 the brain a miniinal amount of blood. The bones of the skull 

 were removed from above. Care was taken to preserve the para- 

 flocculi which lie in bony pockets. 



The brain was severed from the cord by a section at the level of 

 the first cervical nerve — coinciding as a rule with the tip of the 

 calamus as seen from the dorsal aspect. The brain was then 

 raised from the floor of the cranium^ — the nerves being clipped 

 close to the base. The hypophysis was not included. Care was 

 taken to obtain the olfactory bulbs entire. Thus prepared the 

 brain was dropped into a small glass stoppered weighing bottle 

 in which it was weighed to the tenth of a milligram. In this 

 instance, as in the case of all of the other organs, the dissection 

 was made under a glass hood to protect the operator from all 

 drafts which might dry the organ during its preparation. The 

 values for the graph, males only, chart 30 and for table 144 were 

 computed by formulas (9) and (10) corrected for sex. 



The graph for the male alone is given. As will be seen from 

 table 144, for the same body length the female has a slightly 

 lighter brain and this deficiency increases to about 1.5 per cent 

 when the female is of the same body weight. 



Spinal cord weight on body weight. Spinal cord — Technic: 

 Following the removal of the brain (vide ante) the spinal cord 

 was exposed by removing the arches of the vertebrae from neck 

 to sacrum. The filum terminale was found and the cord raised— 

 so that the roots of the spinal nerves could be clipped close to the 

 cord. The mass thus removed with meninges — was placed in a 

 glass stoppered weighing bottle and weighed to the tenth of a 



