CHAPTER 6 



GROWTH OF PARTS AND SYSTEMS OF THE BODY 



IN WEIGHT 



1.- Larger divisions. 2. Systems. 3. Teeth. 4. Blood. 5. Fat. 



1, Larger divisions. The relative growth of the component 

 parts (head, trunk and lunbs) and of the systems (integument 

 hgamentous skeleton, musculature and viscera) has been studied 

 by Jackson and Lowrey ('12). 



The rats were reared at the University of Missouri and fed 

 daily with wheat bread soaked in whole milk^ — a supply of 

 chopped corn being kept constantly in the cages. In addition 

 fresh beef was given once a week. The rats were well grown 

 except at five months and one year, when both sexes were some- 

 what low in body weight — the deficiency bemg most marked in 

 the females. 



The report of the work by Jackson and Lowrey ('12) is given 

 largely in their own words. 



The method of dissection was as follows. The animal was taken 

 in the morning before feeding and killed by chloroform. The gross 

 body weight, and the lengths of bodj^ and tail were recorded. The 

 head (with skin) was then removed (just posterior to the foramen mag- 

 nmn and anterior to the larynx) and weighed. In the meantime, the 

 trunk was suspended and the blood (unmeasured) was allowed to es- 

 cape. Then the viscera were carefullj^ removed and weighed indi- 

 vidually (including brain, spinal cord, eyeballs, thyroid, thymus, heart, 

 lungs, liver, spleen, stomach and intestines, both with contents and 

 empty, suprarenals, kidneys and gonads). Urine was estimated if 

 present. The extremities were separated at the shoulder and hip joints 

 and weighed with skin. The skin (including ears, claws and adherent 

 subcutaneous tissue) was next removed and weighed. The trunk 

 weight was estimated by subtracting the weight of the head and ex- 

 tremities from the net body weight. 



Then the musculature with skeleton was weighed, the few remaining 

 additional structures (genitalia, large vessels, phaiynx and oesophagus, 

 larynx and trachea, and masses of fat connected with the musculature) 



181 



