REGULATION OF GROWTH 



Binswanger (1936), who performed his experiments in dogs. 

 There is real doubt, however, that the thyrotropic hormone 

 which may be found in growth-promoting extracts is of great 

 importance so far as growth effects are concerned.^ 



3. The adrenals. — Moon (1937) found that the injection of 

 the anterior pituitary hormone stimulating the adrenal cortex 

 inhibits somatic growth in young rats of both sexes (the au- 

 thor administered 13-4- "units" over a period of 2-4 weeks). 

 There was little or no effect on the growth of the spleen, liver, 

 kidneys, and alimentary canal. Swingle and others (1936) in- 

 creased the period of survival of adrenalectomized cats by 

 administering a growth-promoting pituitary extract; how- 

 ever, they attributed the beneficial effect of the extract to 

 gonadotropic hormone rather than to a growth-promoting 

 hormone. 



4. The thymus. — The more recent observations suggest 

 that an internal secretion of the thymus promotes growth 

 and development. However, there are no observations indi- 

 cating to what extent such an action may be related to the 

 secretion of a growth-promoting hormone by the pituitary. 

 Rowntree, Clark, and Hanson (1935) reported that the ad- 

 ministration of an extract of the thymus to rats through sev- 

 eral generations finally led to precocious growth and develop- 

 ment which might be very marked early in life. The reverse 

 experiment, thymic deficiency by thymectomy, produced 

 after 2-3 generations a retardation of early growth, especially 

 marked at an age of about i month (Einhorn and Rowntree, 

 1936). The rate of development appeared not to be affected. 

 Parhon and Coban (1936) also found that thymectomy re- 

 tards the growth of fowls (Leghorn and Rhode Island vari- 

 eties). They removed both lobes of the thymus when the 

 birds were about 3 weeks old; at an age of 6 months the thy- 

 mectomized fowls weighed about 30 per cent less than the 

 nonoperated controls. 



*The growth of the liver in the duck in relation to the thyroid, gonads, and hy- 

 pophysis is discussed by Benoit (1937). 



[41] 



