REGULATION OF GROWTH 



ered successful in mammals were made in mice with heredi- 

 tary dwarfism. According to Riddle (1935), and Bates, 

 Laanes, and Riddle (1935), growth in such mice can be pro- 

 duced by thyrotropic extracts or, much less effectively, by 

 lactogenic extracts. They observed a marked synergism of 

 the effect if both extracts were administered. "Follicle-stimu- 

 lating hormone," from the blood of the pregnant mare, was 

 without action. Kemp and Marx (1936) agreed that lacto- 

 genic extracts produce a definite growth of mice with heredi- 

 tary dwarfism. They found thyroxine more effective than 

 thyrotropic hormone, especially in combination with a pitui- 

 tary growth-promoting extract. It is of interest that the 

 degenerative changes in the gonads of such mice were cor- 

 rected and that normal gonads were maintained by a variety 

 of treatments — growth-promoting extract or lactogenic ex- 

 tract or thyrotropic extract or thyroxine. 



However, there are numerous objections to the view that 

 the thyrotropic hormone or the lactogenic hormone or both 

 account for the principal effects of growth-promoting ex- 

 tracts. Conclusions drawn from experiments in pigeons prob- 

 ably have only a limited significance in mammals. Thyro- 

 tropic hormone antagonizes the growth-promoting effect of 

 the lactogenic hormone in pigeons (Bates, Riddle, and Lahr, 

 1937)5 whereas the two hormones were found to have a syner- 

 gistic effect on growth in the dwarfed mouse. Hypophysec- 

 tomized rats are very sensitive toward pituitary growth- 

 promoting extracts; yet no investigator has succeeded in 

 causing such animals to grow by administering either lacto- 

 genic hormone or thyrotropic hormone or a combination of 

 the two. Although it must be admitted that partially refined 

 growth-promoting extracts are usually more certain and more 

 persistent in their action than highly purified preparations, 

 the same remark applies to comparisons of the action of such 

 partially refined extracts with that of the combined adminis- 

 tration of lactogenic and thyrotropic hormone to mice with 

 hereditary dwarfism. Bates, Laanes, and Riddle (1935) ob- 



[33] 



