STEROIDS AND GROWTH 



391 



Estrogens and epiphyseal cartilage. The development of the proxi- 

 mal epiphyses of the tibia in normal and hypophysectomized rats has 

 been studied by a number of investigators (Ingalls, 1941; Ingalls and 

 Hayes, 1941; Ray, Evans, and Becks, 1941; Becks, Kibrick, Marx, and 

 Evans, 1941). Becks, Simpson, and Evans (1945, a, b) have paid par- 

 ticular attention to the changes occurring in the normal female rat and 

 the hypophysectomized female rat. These authors demonstrated that a 

 very rapid narrowing of the cartilage plate occurs between the ages of 

 40 days and 65 days in normal females. This marked decrease in the 

 width of the epiphyseal plate occurs at the beginning of sexual matur- 

 ity in the strain of animals used and is reflected further by a marked 



3-4 4-5 5-6 6-7 7-8 8-9 910 1011 11-12 1213 13-14 1415 years 



Figure 3. Urinary excretion of total estrogen in international units in boys and girls of 

 different ages, (o female; • male.) (Data from Nathonson, Towne, and Aub, 1941.) 



