90 GROWTH OF PARTS AND ORGANS 



the graphs in chart 8 and for the table 68 were determined by 

 formulas 4 and 5. The tail in the female is relatively longer 

 than in the male. Hatai (MS 14). 



4. Following the plan of grouping the organs according to the 

 manner of their growth we shall first consider the weights of the 

 brain, the spinal cord and both eyeballs. All of these organs have 

 an early rapid growth. 



Brain weight on body weight. Technic: The rat was first 

 eviscerated — this leaves in the brain a minimal amount of blood. 

 The bones of the skull were removed from above — the meninges 

 being left intact. Care was taken to preserve the 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 milli- 

 gram. In this instance, as in the case of all of the other organs, 

 the dissection was made under a glass hood to protect the oper- 

 ator from all drafts which might dry the organ during its prepa- 

 ration. The values for the graph, males only, chart 9 and for 

 table 68 were computed by formulas (6) and (7). 



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

 table 68, for the same body length the female has a slightly 

 lighter brain and this difference 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 milligram. The values for the graph, males only, in chart 9 

 and for table 68 were computed by formula (11). Donaldson 

 ('08), ('09); Hatai, ('09a). 



