ACTIVE PRINCIPLES OF PARS NEURALIS 



considered to be identical with the pressor principle) can be 

 assayed accurately by using the isolated ileum of the guinea 

 pig. As little as the equivalent of i unit in a liter of Tyrode's 

 solution can be detected. 



3. The principle inhibiting water diuresis {at present con- 

 sidered to be identical with the pressor principle). — The inhibi- 

 tion of water diuresis in unanesthetized animals has been 

 used as a means of assaying posterior-lobe extracts in man, 

 the dog, the rabbit, the rat, and the mouse. The adult hu- 

 man being is exceedingly sensitive; the effects of a total sub- 

 cutaneous dose as small as 0.2 unit can be detected (Burn). 

 The dog is more sensitive than the rabbit (Bijlsma, 1925; 

 Kestranek, Molitor, and Pick, 1925). 



The suitability of the dog with a fistula of the bladder 

 for the assay of the diuresis-inhibiting principle also has been 

 studied by Molitor (1926), Bijlsma, Burn, and Gaddum 

 (1928), Glaubach and Molitor (1932), and Penau and 

 Simmonet (1934). Apparently the response of dogs varies 

 considerably; therefore, if the extracts are to be given sub- 

 cutaneously, small animals which can be used in larger num- 

 bers should be employed. Stehle (^1934) found that, by the 

 intravenous injection of the extract into dogs with bladder 

 fistulae, o.ooi unit of the diuresis-inhibiting extract could be 

 detected. Bentz, Marx, and Schneider (1934) also performed 

 assays in the dog by administering extracts intravenously. 



Accurate assay of the diuresis-inhibiting hormone probably 

 can be performed most conveniently by using the mouse or 

 the rat. Large enough groups of animals can then be used so 

 that the assay will take into account the naturally occurring 

 variations in response. Gibbs (1930) was the first to perform 

 assays in mice. He administered tap water intraperitoneally 

 and injected the posterior-lobe extract subcutaneously. He 

 then compared the rate of secretion of the urine by control 

 mice (water only) with that by mice receiving both water 

 and the extract. This method has been extended and refined 



{3^\ 



