THE PITUITARY BODY 



hand, is among the most resistant. This fact helps to explain 

 the success of Evans and Long (1921-22) in demonstrating 

 the growth-promoting properties of crude anterior pituitary 

 extracts in the rat; if they had attempted this in the guinea 

 pig their extract would have caused, at least initially, a loss 

 of weight due to hypersecretion by the thyroid. Thurston 

 (1933) has given the most complete account of species dif- 

 ferences in the response to thyroid-stimulating hormone. The 

 mouse and rat are the least sensitive; the guinea pig is the 

 most sensitive; intermediate in the order of increasing sensi- 

 tivity are the rabbit, cat (and pigeon). The typical anatomi- 

 cal effects of extract administration in the guinea pig, de- 

 scribed in the paragraph below, are modified in the cat in 

 which the chief change consists in a diminution in the amount 

 of colloid. Aron (1932), Houssay, Novelli, and Sammartino 

 (1932), Houssay (1932), Kleine (1932), and Loeser (1934) re- 

 ported in less detail on similar differences in response among 

 different animals. 



Like Aron (1929) most investigators have found the re- 

 sponse of the guinea pig is most marked in the young animal 

 (weight, 150-200 g.) and that older animals are relatively in- 

 sensitive. According to Friedgood (1935) the response of the 

 female guinea pig is more intense and persists longer than 

 that of the male. The extract is ineffective by mouth and 

 must be given parenterally (Janssen and Loeser, 1931; An- 

 derson and Collip, 1934). As soon as 2 hours after injection 

 changes can already be observed in the thyroid according to 

 Eitel and Loeser (1932). It has usually been the practice to 

 inject the anterior-lobe extract for several days and to sacri- 

 fice the animals about 24 hours after the last injection. The 

 anatomical changes, which depend to a considerable extent 

 on the amount of material injected, were first described by 

 Aron (1929) and Loeb'° and Bassett (1929), whose findings 



'° The experiments of Loeb and his co-workers with Armour'^s pituitary tablets 

 are not considered because these tablets appear to contain thyroid as shown in 



f26ol 



