THE DUCTLESS GLANDS 415 



But, as pointed out by Schafer, it is probable that the blood of 

 an animal dying slowly as the result of any disease would be to 

 some extent toxic, and that the toxic principles would more 

 powerfully affect animals the resisting power of which had been 

 lessened by a recent severe operation. Further, the suprarenals 

 produce a material which has entirely different properties from 

 those stated to be possessed by the blood of animals deprived of 

 their capsules. 



The " internal-secretion " theory is briefly as follows : The 

 medulla of the suprarenal capsules is continually secreting into 

 the blood an active material, adrenalin, or better, as Schafer 

 suggests, " adrenin," which is beneficial in maintaining the tone 

 of muscular tissues, and particularly that of the vascular system. 

 In this view the absence of the active substance in animals 

 deprived of their suprarenal capsules, and in cases in the human 

 subject in which both capsules were involved in disease, is the 

 true cause of the symptoms which manifest themselves in these 

 circumstances. It follows, according to this theory, that 

 Addison's disease is due to suprarenal insufficiency — to an 

 inadequate supply of the suprarenal secretion. 



Although this theory of internal secretion is the one which 

 is now most generally accepted, and which appears to have 

 the balance of probability on its side, one is bound to admit 

 that the direct evidence of the actual secretion of material 

 into the blood streams is not very great. The blood from the 

 suprarenal veins is stated to produce physiological effects greater 

 than those obtained from other blood, and recently experiments 

 have been performed under the direction of the present writer 

 which seem to point definitely to a secretion from the medulla 

 into the veins of the gland (17). But it must be admitted that, 

 in view of our total ignorance of the functions of the cortex, and 

 our doubt as to whether the two portions are related, the time 

 is not ripe for any very definitely formulated views as to the 

 functions of the suprarenal capsules. 



(ii) The Thyroid and Parathyroid Glands 



(a) Effects of ablation and disease. — Our knowledge of this 

 subject is not based upon so secure a foundation as a perusal of 

 modern text-books would lead one to suppose, and there can be 

 little doubt that there has been in some directions undue haste 

 in correlating clinical experience with the results of experimental 



