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 myxcedema 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. Soc. de biol., Paris, 1891, p. 307 ; see also Gley, ibid., 1894, 

 p. 192 ; and Masoin, ibid., p. 105. 



3 Gley, Arch, de physiol. norm, etpath., Paris, 1894, p. 484. 



4 Oliver and Schafer, Journ. Physiol., Cambridge and London, 1895, vol. xviii. p. 277. 



5 Croonian Lectures, Lancet, London, 13th June 1896. 



6 Leichteustern, Deutsche med. IVchnschr., Leipzig, 1894, No. 50. See on the physio- 

 logical action of thyroid extract, Ewald, loc. tit. ; Donatti, Virchow'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. 



7 Michaelsen, Arch. f. d. ges. Physiol., Bonn, 1889, Bd. xlv. S. 622. 



8 Journ. Physiol., Cambridge and London, 1894, vol. xvi. p. 378. 



