ASSAY OF CORTICAL HORMONE 249 



for the assay of cortical extracts. De Meio and Lewis recom- 

 mended the use of morphine as the toxic agent. As shown by 

 Leloir and Novelli, 387 the use of morphine does not lend itself 

 for an exact assay. This is also true of the use of histamine, 

 diphtheria toxin, and other drugs or physical agents. The 

 weakness of these methods lies in the fact that the sensitivity 

 of different animals (normal or adrenalectomized) varies 

 greatly towards a given drug. An excessively great number 

 of animals must consequently be used in order to obtain 

 approximately representative results. The reaction of the 

 adrenalectomized animal will be even more variable because 

 it will depend upon the degree of insufficiency existing at the 

 time of injection of the drug. This is an extremely variable 

 quantity. Even if one were to fix empirically the conditions of 

 the experiment with a high degree of constancy, the method 

 would still remain inexact and require the operation and 

 sacrifice of scores of animals in order to attain even approxi- 

 mately accurate results. A fundamental defect of all methods 

 based on the increased susceptibility to toxic agencies after 

 adrenalectomy is the fact that such increased sensitivity is in 

 part due to the secondary effects of adrenal insufficiency in 

 lowering the general resistance of the body. The methods, 

 therefore, only indirectly measure the degree of adrenal in- 

 sufficiency. 



The working capacity of adrenalectomized rats is decreased 

 in adrenal insufficiency. It has been suggested that this 

 property be used to standardize cortical extracts. 191 The ob- 

 jections raised in the preceding paragraph are also applicable 

 to this method of assay. 



METHODS BASED ON THE NON-PROTEIN NITROGEN LEVEL 

 OF THE BLOOD 



The second method which has been used in assaying adrenal 

 cortical extracts is based on determining the non-protein 

 nitrogen of the blood of the adrenalectomized dog, as suggested 



