CHAPTER V 



THE THYROID AND PARATHYROIDS (c&ntinued) 



Effects of Increase of Thyroid Secretion: Hyperthyroidism 



The effects of a too great amount of the thyroid autacoids in the circulating 

 blood can be investigated either by their introduction directly into the 

 circulation or indirectly by other channels, such as the alimentary canal : 

 or by studying the symptoms of affections in which there is reason to 

 believe that an excess of these autacoids is being secreted by the gland. 



Effects of Administration of Thyroid Extract or Juice 



The immediate result of intravenous injection (fig. 24) is to produce a 

 marked but evanescent fall of blood-pressure, which is mainly due to 

 dilatation of the peripheral vessels. This effect is probably specific, 



Fig. 24. — Effect upon the blood-pressure of injecting thyroid extract intravenously. 



lp., arterial pressure ; a., abscissa ; t., time in one-second intervals. (From the British Medical 

 Journal, Aug. 10, 1895.) 



although somewhat similar results are obtained with extracts of many 

 other organs (see pp. 9, 10). 



The fall of blood-pressure caused by thyroid extract is often preceded 

 by a slight rise. The fall is just as well marked after administration of 

 atropine as before : it is therefore not due to vagus action. 



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