270 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



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

 to some, the office of these bodies is to remove some toxic substance or sub- 

 stances which normally accumulate in the blood as the result of the body- 

 metabolism. If the thyroids or parathyroids are extirpated, the correspond- 

 ing substance then increases in quantity and produces the observed symptoms 

 by a process of auto-intoxication. In support of this view there are numerous 

 observations to show that the blood, or urine, or muscle-juice of thyroid- 

 ectomized 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 and parathyroids secrete each 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 properly prepared 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, per- 

 haps, whether this material acts by antagonizing toxic substances produced 

 elsewhere in the bodv or by directly influencing the body metabolism. For 

 a more specific theory of the functional value of the thyroids proposed by 

 ('von'-' reference must be made to original sources. Much work has been 

 done to isolate the beneficial material of the thyroid, particularly in relation 

 to the therapeutic use of the gland in myxoedema 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 3 that the gland material 

 may be boiled for a long period with 10 per cent, sulphuric acid without 

 destroying the beneficial substance. This observer has succeeded in isolating 

 from the gland a substance to which the name iodothyrin is given, which is 

 characterized by containing a relatively large percentage (!'.."> per cent, of the 

 dry weight) of iodine, and which preserves in large measure the beneficial 

 influence of thyroid extracts in cases of myxoedema and parenchymatous 

 goitre. In the parathyroid tissue the same material is contained in relatively 

 larger quantities. This notable discovery shows that thyroid tissue has the 



1 See Schaefer: "Address on Physiology," annual meeting of the British Medical Associa- 

 tion, London, July-August, IS').". 



: Archives de Phyaiologie, 1898, p. 618. 



8 Zeitschrift fur physwlogische Chemie, l x '.'t'., Bd. xxi. >S. 319. 



