§1.6 IDENTIFICATION 15 



each separately (4), it is shown that ACTH is the only effective 

 substance. 



At this point it still remains an open question as to whether the two 

 hormones that have been identified have independent actions, or 

 whether one is direct and the other indirect, as it would be if one were 

 an endocrinokinetic hormone. 



Experiments 5 to 7. The results of these further experiments and their 

 controls give the minimum of information upon which these questions 

 can be decided. Cortex extract alone is effective in the absence of 

 both sources (7), and is therefore the direct metabolic hormone, whereas 

 ACTH is ineffective (6), unless the cortex tissue is present (4). Since 

 the unstimulated cortex is ineffective (3), the action of ACTH must be 

 to stimulate the cortex to secrete (as in the normal animal, and in 

 experiments \a and 4). 

 Conclusion: ACTH is, therefore, the endocrinokinetic hormone stimulating 

 the secretion of a metabolic hormone from the adrenal cortex. 



the experimental investigation becomes more complex. The 

 tabulated theoretical scheme for a set of experiments, to show 

 the relation of a metabolic hormone from the adrenal cortex and 

 the adrenocorticotrophic hormone, ACTH, from the adeno- 

 hypophysis (Adhp. Table 2), is given as an indication of the mini- 

 mum number of experiments involved. 



Taking ''death" or "survival" of the animal as the criterion of 

 the hormone's action is obviously much too crude, and should be 

 replaced by some surer physiological test of the metabolic activi- 

 ties affected, such as the measurement of blood-sugar ; but in that 

 case, the opposing action of insulin has also to be taken into 

 account (§§4.2 and 5.2). 



For obvious reasons of space it will not be possible in the cases 

 cited below to give full details and results of all the experiments 

 upon which the conclusions are based; but an attempt will be 

 made to give some of the clearer examples in enough detail to 

 indicate how far the technique of the original work was satis- 

 factorily controlled. 



