THE THYROID GLAND AND THE ADRENALS. 147 



ducing no marked effect; and in rabbits and other herbivorous 

 animals removal is said never to be followed by any of the 

 above results. It has been urged that the symptoms, when 

 seen, are the effects not of the mere absence of the organ, but 

 of the mischief set up by the operation in adjoining structures, 

 more especially in the laryngeal nerves and vagus trunks; 

 but this does not seem a valid explanation. If, as suggested 

 above, certain metabolic processes are normally going on in 

 the organ, we may fairly suppose that, in the absence of the 

 organ, the interruption of the normal sequence of chemical 

 change would throw upon the circulation certain strange sub- 

 stances which, acting like a poison, might produce the nervous 

 symptoms, throw into disorder the nutrition of various tissues, 

 and finally bring about death. We may further explain the cases 

 where symptoms are absent by supposing that, for some reason 

 or other, "things have taken a different turn": the particular 

 poisonous substances have not made their appearance, but in- 

 nocuous ones have taken their place; and we know how slight 

 a change in chemical composition may turn a poison into an 

 inert body. This, of course, remains a mere supposition until 

 we can state what the exact metabolic processes are, and name 

 the substances which work the mischief; but it seems more 

 reasonable to accept such a provisional supposition than to 

 conclude that the thyroid may be removed without producing 

 any effect whatever on the organism. An animal without a 

 thyroid may appear perfectly well, because the circumstances 

 to which it is exposed do not happen to test the imperfection 

 from which it is really suffering, just as a man's inability to 

 swim may not be apparent until he happens to fall into the 

 water. The animals which do succumb to the operation of 

 removal of the organ are, for some reason or other, put to the 

 test, and are found wanting. The very discordance of the ex- 

 perimental results points to the physiological moral that the 

 phenomena which we are as yet able to observe form, as it 

 were, a mere surface covering intricate processes at present 

 wholly, or nearly wholly, hidden from us." 4 



If the data recorded in the last chapter concerning the 



* The italics are our own. 



