STRUCTURES AND PROCESSES OF OBSCURE NATURE. 467 



above kinds of animal, no serious symptoms follow, even the total extirpation 

 of the organ producing no marked effect ; and in rabbits and other her- 

 bivorous 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 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 substances 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 substance have not made their 

 appearance, but innocuous 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 supposi- 

 tion, 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 want- 

 ing. The very discordance of the experimental results points the physio- 

 logical 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. 



The above experimental results receive additional interest and at the 

 same time support from clinical experience. The connection between goitre 

 and cretinism the latter disease being, broadly speaking, a result of dis- 

 ordered nutrition telling largely on the nervous system has long been 

 recognized ; and attention has also been called to some tie between disease 

 of the thyroid and a morbid condition, known as myxoedema, in a certain 

 number of cases of which mucin or a mucin-like body has been found in 

 great excess in the skin and in other tissues. In monkeys the removal of 

 the thyroid has, in some cases, been followed, besides the symptoms men- 

 tioned above, some of which resemble those of myxoedema, by an accumu- 

 lation of mucin or a mucin-like body in the skin and various tissues. It is 

 very difficult not to connect this with the formation in the thyroid of colloid 

 material in the contents of the alveoli. But we know so little about the 

 nature of mucin and its allies, about their real relations to more ordinary 

 proteid substances, and about the part which they play in physiological pro- 

 cesses, that any views as to the exact connection between the presence of 

 mucin in the tissues at large and changes taking place in the thyroid must 

 be at present to a large extent speculation. 



The large vascular supply of the thyroid, and the phenomena of a 

 disease known as exophthalmic goitre, in which vascular enlargement 

 of the thyroid is associated with cardiac symptoms, and other vascular 

 disturbances, especially of the head, have suggested that, apart from 

 metabolic processes, the circulation in the thyroid may, perhaps in a 

 more or less mechanical way, be connected with and influence the cir- 



