180 GROWTH IN TOTAL BODY WEIGHT 



atrophied, while in single isolation the surviving ovary is hyper- 

 trophied^ — Stotsenburg ('17). 



6. Senescence. In the colony at the Institute albino rats 

 rarely live more than 40 months. Commonly lung disease 

 (rat pneumonia) is the immediate cause of death. After two 

 years the animals tend to become slow and decrepit. They 

 eat less, sleep much and the hair become thin, rough and dry. 

 The angle between the nasal and frontal bones is increased, 

 giving the "roman nose" effect. The female usually ceases to 

 breed at 18 to 20 months. The end of the breeding time in the 

 males is not known. The loss in body weight in old animals 

 is very marked, but whether body length is also duninished is 

 not known. 



As shown in table 156 and chart 49-Nos. 1-21 the relative 

 weights of the organs decrease with advancing age, but just how 

 great this decrease may be in rats, three years old or older, has 

 yet to be determined. 



GROWTH IN TOTAL BODY WEIGHT ACCORDING TO AGE : REFERENCES 



Introduction. Przibram, '22. 



Growth before birth. Huber, '15 a. Stotsenburg, '15. 



Growth between birth and maturity. Donaldson, '06, '12 c, '15. Donaldson, 

 Dunn and Watson, '06. Dunn, '08. Ferry, '13. Greenman and Duhring, '23. 

 Jackson, '13, King, '15, '15 a. Robertson, '08. Watson, '05. 



Modifications of growth in total body weight and in organs. Donaldson, '11a. 

 Greenman and Duhring, '23. Hammett, '23. Hart and McCollum, '13, '14. 

 Hatai, '03 a, '04 a, '07 a, '08, '13 a, '15, '15 b. Henn, '20. Jackson, '15, '15 a, 

 '15 b. Jackson and Stewart, '18, '19, '20. King, '16. Kudo, '21, '21 a. Mor- 

 gulis, '11. Osborne and Mendel, '14 d, '15 d, '16. Paul, '06. Reed, '21. Slon- 

 aker and Card, '23. Smith and Ascham, '22. Stewart, '16, '18, '19. Stot- 

 senburg, '09, '13, '17. Watson, '06, '06 a, '06 b. Watson and Gibbs, '06. Wat- 

 son and Lyon, '06. Watson, '07 a, '07 b, '07 c, '07 d, '10, '12. Watson, J. B., 

 '05. 



Senescence. Ruzicka, '22. 



