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CELLS, TISSUES, AND ORGANISMS 



taken two years later. During this interval the hypophysectomized ani- 

 mal grew not at all, while his partner continued to increase in size and 

 to mature in the normal fashion, weighing 8.4 kg. at the time the photo- 

 graph was taken. 



The observation that hypophysectomy leads to an arrest of growth 

 was first made in the dog by Aschner (1912) in a series of carefully 

 conceived and executed experiments. His findings were most convinc- 

 ingly confirmed in the rat by Smith, who in 1926 began a classic series 

 of investigations dealing with the physiology of the pituitary gland 

 (Smith, 1930). Smith's early studies, aided by his development of a 

 relatively simple and reliable surgical technique for hypophysectomy 

 in the rat, created a new sphere in mammalian endocrinology with the 

 pituitary gland at its center. 



Not only does the hypophysectomized animal cease to grow, but, 

 if the operation is performed before the onset of puberty, it remains 

 infantile sexually as well as somatically. Its baby fur and deciduous 

 dentition are retained for prolonged periods, while the entire repro- 

 ductive tract remains undeveloped as a consequence of gonadal inac- 



Figure 1. Effects of hypophysectomy in the immature rhesus monkey. (See 

 text for details.) 



