36 The Endocrine Organs 



Asher states that the fall of blood-pressure does not occur in the rabbit. I have, 

 however, occasionally obtained it in that animal, but usually the fall is absent and 

 a slight rise alone apparent. 



Asher and Flack found that the prior injection of thyroid extract in the rabbit 

 increases the excitability of the cardiac vagus and of the depressor. I have not 

 been able to confirm this result either in the rabbit or in the cat or dog, although, in 

 the last two, if depressor fibres are stimulated at the same time that thyroid extract 

 is injected into a vein the fall of blood-pressure is greater than with either of these 

 by itself. This is, however, an effect of summation, as is shown by the circumstance 

 that in those cases in the rabbit in which a slight rise is produced by thyroid 

 extract instead of a fall, the combined effect of depressor and thyroid extract is less 

 than that of the depressor alone. 



Given by the mouth in the human subject thyroid extract produces lower- 

 ing of the bleed-pressure. 1 Large doses are followed by tachycardia (rapid 

 pulse), often with some irregularity ; nervous excitability ; flushing of the 

 skin, with feeling of heat ; increase of perspiration ; and increase of nitrogen 

 metabolism. If long continued the fat of the body is diminished and 

 glycosuria may be caused. Alimentary glycosuria is also more easily 

 produced than normally. There is considerable wasting, although the 

 appetite is increased. There are often digestive disturbances. In extreme 

 cases there may be exophthalmos and other effects referable to cervical 

 sympathetic excitation, such as dilatation of the pupil and (in animals) re- 

 traction of the third eyelid ; psychical excitement ; sleeplessness ; tremors 

 of the limbs ; in short, most of the symptoms of exophthalmic goitre. The 

 addition to the food of animals of even a small amount of thyroid gland 

 has the effect of increasing nitrogenous metabolism, as shown by the 

 increase of nitrogen in the urine. This is accompanied by a corresponding 

 increase in food consumption. Some of the additional nitrogen thus 

 ingested is retained in the body, but this is compensated for by increased 

 fat consumption, so that the difference in growth curve of the thyroid-fed 

 animals and the controls is but slight. With large doses of thyroid there 

 soon ensues marked loss of weight, due both to increased nitrogen elimina- 

 tion and loss of fat. There is also an increased respiratory exchange. 



The colloid contents of the thyroid vesicles are augmented by the 

 ingestion of much thyroid substance. 



CLINICAL EVIDENCE 



Exophthalmic Goitre. This affection, first described by Parry (1825) 

 and connected by him with the thyroid, is also associated with the names 

 of Graves (1835) and Basedow (1840), both of whom called special attention 

 to the symptoms. The name exophthalmic goitre expresses its most 

 prominent signs (fig. 25). The disease is usually accompanied by consider- 

 able enlargement of the thyroid. According to Moebius and Greenfield 



1 In diabetic subjects it is said to cause the opposite result an effect lasting for several 

 days. 



