130 



VITAMINS A AND CAR0TP:NP:S 



daily, given to 10-day-old guinea pigs during the period of excess vitamin 

 A intake, does not modify the skeletal responses. 



The study of hyper\'itaminosis A in the chick has covered only the first 



Fig. 41. Hypervitaminosis A in the chick. Cross section of sacral vertebra through 

 midportion of the rhomboidal fossa and the glycogen body. To illustrate the compact 

 bone formation characteristic of hypervitaminosis A in this species and almost com- 

 plete absence of epiphyseal cartilage. Compare with Fig. 42, showing the same region 

 of a vitamin A-deficient chick of the same age, and Fig. 43, showing a vertebra at a 

 higher level from an age control chick which shows the normal textiu'c of th(> l)ones of 

 the vertebrae. 



32 days after hatching, a period in which the I'eplacement of cartilage in the 

 long bones is far from complete. Acceleration of endochondral l)one forma- 

 tion and earlier establishment of epiphyseal cartilage plates are results. 

 The pattern of remodeling se(iuence changes awaits knowledge of the nor- 

 mal. Accelerated comi)act l)one formation in the chick is outstandingly 

 more active than in mammals. Il occin-s in all bones but is most strikingv 



