SECRETION. 209 



It follows from these various observations that the thyroid glands play a 

 very important part of some kind in the general metabolism of the body 

 Two views prevail as to the general nature of their function. 1 According to 

 some the office of the thyroids is to remove some toxic substance which nor- 

 mally accumulates in the blood as the result of the body-metabolism. If the 

 thyroids are extirpated this substance then increases in quantity and produces 

 the observed symptoms by a process of auto-toxication. In support of this 

 view there are numerous observations to show that the blood, or urine, or 

 muscle-juice of thyroidectomized animals has a toxic effect upon sound animals. 

 These latter results, however, do not appear to be marked or invariable, and 

 in the hands of some experimenters have failed altogether. The second view 

 is that the thyroids secrete a material, a true internal secretion, which after 

 getting into the blood plays an important and indeed essential part in the 

 metabolic changes of some or all of the organs of the body, but especially the 

 central nervous system. In support of this view we have such facts as these : 

 Injections of thyroid extracts have a beneficial and not an injurious influence; 

 there is microscopic evidence to show that the epithelial cells participate 

 actively in the formation of the colloid secretion and that this secretion 

 eventually reaches the blood by way of the lymph-vessels; the beneficial 

 material in the thyroid extracts may be obtained from the gland by methods 

 which prove that it is a distinct and stable substance formed in the gland, as 

 we might suppose would be the case if it formed part of a definite secretion. 

 This latter fact, indeed, amounts to a proof that the important function of the 

 thyroids is connected with a material secreted within its substance ; but it may 

 still be questioned, perhaps, whether this material acts by antagonizing toxic sub- 

 stances produced elsewhere in the body or by directly influencing the body- 

 metabolism. Much work has been done to isolate the beneficial material of the 

 thyroid, particularly in relation to the therapeutic use of the gland in rnyxce- 

 dema and goitre. The mere fact that feeding the gland acts as well as injecting 

 its extracts shows the resistant nature of the substance, since it is evidently not 

 injured by the digestive secretions. It has been shown also by Baumann 2 

 that the gland material may be boiled for a long period with 10 per cent, sul- 

 phuric acid without destroying the beneficial substance. This observer has 

 succeeded in isolating from the gland a substance to which the name thyro- 

 iodin is given, which is characterized by containing a relatively large per- 

 centage (9.3 per cent, of the dry weight) of iodine, and which preserves in 

 large measure the beneficial influence of thyroid extracts in cases of myxce- 

 dema and parenchymatous goitre. This notable discovery shows that the thy- 

 roid tissue has the power of forming a specific organic compound of iodine, and 

 and it is possible that its influence upon body-metabolism may be connected 

 with this fact. In a later communication by Baumann and Roos 3 it is stated 

 that the thyroiodin is contained within the gland mainly in a state of combi- 



1 See Schafer : " Address on Physiology," annual meeting of the British Medical Association, 

 London, July-August, 1895. 



2 Zeitschrift fur physiologische Chemie, 1896, Bd. xxi. S. 319. 3 Ibid., S. 481. 



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