PARS GLANDULARIS AND LACTATION 



tihormone" but even seemed to augment the action of the 

 hormone. 



The assay of lactogenic hormone. — The only satisfactory- 

 methods of assaying the lactogenic hormone are based upon 

 the response of the crop-glands of pigeons — a test introduced 

 by Riddle and his colleagues. After the injection of extract 

 containing lactogenic hormone, the crop-glands undergo 

 hypertrophy which may be limited to only one of the two 

 glands, provided that not too large a dose is injected into 

 the skin overlying the gland. Pigeons of the same stock vary 

 greatly, of course, in sensitivity. Some varieties of pigeons 

 are more suitable than others; Bates and Riddle (1935) found 

 that a tenfold variation in sensitivity may be encountered in 

 different races of pigeons (see also Evans, 1 937) . Wolff ( 1 937) 

 concluded that the response of young birds is more regular 

 than that of adults. Birds of either sex can be used. 



The effect of a dose of lactogenic hormone depends upon 

 the route of absorption. The greatest response follows the 

 intracutaneous administration of extract over a crop-gland. 

 The dose causing a given response is about i per cent of that 

 necessary, if injection is subcutaneous, intramuscular, or 

 intraperitoneal (Lyons and Page, 1935; Bates and Riddle, 

 1936; and Chasin, 1936). According to Bates and Riddle 

 (1936), the relative efficacy of injected hormone is approxi- 

 mately the following: intracutaneous, 1,000; subcutaneous, 

 10; intramuscular, 2; intraperitoneal, 1.3; and intravenous, 

 0.9. 



Varous authors^' have devised methods of assay and have 

 often determined the relationship between dose and response, 

 which usually is given in terms of crop-gland weight, some- 

 times in relation to body-weight. Potency also may be esti- 

 mated from the percentage of birds in which a minimum 

 response is produced. Probably few investigators will oppose 

 the view that a standard preparation, perhaps crystalline 



" Bates, Riddle, and Lahr (1936), Dyer (1936), McShan and Turner (1936), 

 Lyons (1937), Rowlands (1937). 



[169] 



