EFFECT OF THYROID JUICE. 943 
render innocuous. 1 According to this, the function of the thyroid 
would be primarily excretory. This view is supposed to be sup- 
ported by the observation, that the urine of animals becomes, after 
removal of the thyroid, more toxic than that of normal animals, 2 and that 
the blood is toxic for other animals, and especially for those which have 
already had the thyroid removed, although this operation may have 
been performed only a short time previously, and before the 
symptoms of thyroidectomy have had time to develop. It is not stated 
what the probable nature of this substance is, or by what tissues it 
may be formed. 
Effect of thyroid juice. — The " internal secretion " theory would 
explain the phenomena of extirpation as due to the absence of a 
secretion which is formed within the thyroid or parathyroids, and 
passes from them into the blood ; a secretion which is necessary for 
certain of the metabolic processes of the animal body, and especially 
for those connected with the nutrition of the central nervous system 
and of the connective tissues. That this view of the function of 
the thyroid, which was the one given originally by Schiff, is in the 
main the true one, is shown by the fact that beneficial and not 
toxic effects follow the exhibition of thyroid juice, both in cases of 
thyroidectomy in animals and in myxoedema and other affections in 
man. Moreover, extracts of thyroid gland produce distinct physiological 
effects in the normal subject. 3 If a decoction of the gland be injected 
into a vein, the blood pressure markedly falls (Fig. 85), although the 
beats of the heart remain at about the same rate and of the same 
strength as before. 4 This lowering of the blood pressure is not, however, 
peculiar to the thyroid, but occurs with extracts of some other 
secreting glands. But it has been shown by G. Oliver, 5 that the 
exhibition of thyroid juice or other preparations of thyroid seems to 
possess a specific tendency to increase the calibre of the radial artery in 
the human subject. It would seem, therefore, that the juice of the 
thyroid, and extracts which are obtained from the gland, have a distinct 
action upon the vascular system. It has further been noticed that feeding 
with thyroid tends to cause increased metabolism in the body, accom- 
panied by diuresis and diminution of fat, so that it has been proposed as 
a cure for obesity. 6 Thyroidectomy alters the conditions of the gaseous 
exchange, 7 and this in all probability by an indirect effect through 
the vasomotor system. Lorrain Smith 8 found that in animals which 
have been deprived of the thyroid body, the reaction to changes of 
temperature is abnormally rapid. When normal animals are exposed to 
a cold atmosphere, the production of carbon dioxide becomes increased, 
consistently with the increased oxidation which is necessary to cause 
1 Horsley, Proc. Roy. Soc. London, 1886, vol. xl. p. 6 ; Brit. Med. Journ., London, 
1892 ; Blumenreich and Jacoby, Arch. f. d. ges. Physiol., Bonn, 1896, Bd. xiv. S. 1. 
2 Laulanie, Compt. rend. Sot. de biol., Paris, 1891, p. 307 ; see also Gley, ibid., 1894, 
p. 192 ; and Masoin, ibid., p. 105. 
3 Gley, Arch, de physlol. norm, etpath., Paris, 1894, p. 484. 
4 Oliver and Schiifer, Journ. Physiol., Cambridge and London, 1895, vol. xviii. p. 277. 
5 Croonian Lectures, Lancet, London, 13th. June 1896. 
6 Leichtenstern, Deutsche mcd. Weknschr., Leipzig, 1894, No. 50. See on the physio- 
logical action of thyroid extract, Ewald, loc. cit. ; Donatti, Virehow's Archiv, 1896, Suppl. 
Bd. cxliv. S. 253 ; Berkeley, Johns Hopkins Hosp. Bull., Baltimore, July 1897. Berkeley 
examined the nerve centres of animals which had died from prolonged" administration of 
thyroid extract, but could find no evidence of any changes in the nerve cells. 
" T Michaelsen, Arch. f. d. ges. Physiol.. Bonn, 1889, Bd. xlv. S. 622. 
8 Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 378. 
