20 PHYSIOLOGY CHAP. 



thyroid, in all cases in which there is danger of plethora or 

 cerebral anaemia. In the first case, by dilatation of its vessels, 

 the thyroid receives the excess of blood which would otherwise 

 reach the brain ; in the second, by contraction of its arteries, it 

 determines a greater flow of blood to the cerebrum. Guyon (1868) 

 adopted a more complicated, but analogous point of view, affirm- 

 ing that every increase in cerebral blood-pressure produces an 

 augmentation in the volume of the thyroid (probably by passive 

 vascular dilatation) which causes compression of the carotids, 

 and prevents the blood from flowing in large quantities to the 

 brain. Finally, Meuli (1884) attempted to give an experimental 

 basis to the Schreger-Liebermeister theory, demonstrating by a 

 series of measurements upon himself that the circumference of 

 the neck varies considerably with the position of the body, these 

 variations being maximal at the level of the thyroid region. 



Without denying whatever may be true in this theory, as put 

 forward by Liebermeister, its importance must not be exaggerated. 



It is obvious that any regulatory or compensatory influence on 

 the cerebral circulation which may be attributable to the thyroid 

 arteries can have nothing to do with the specific function of the 

 thyroid as a glandular organ of internal secretion. 



The cousins Keverdin and Kocher (1883), who, as we have seen, 

 were the pioneers of research into the physiology of the thyroid 

 as a glandular organ, were not happy in their first attempt to 

 explain tetany and cachexia thyreopriva in man. According to 

 Keverdin, this characteristic syndrome depended on disturbances of 

 innervation caused by lesions of the nerve trunks in the course 

 of extirpating the thyroid organ. According to Kocher, on the 

 contrary, the ligation of the great thyroid vessels in excision of 

 this body produced on the one hand a considerable diminution 

 in the lumen of the trachea, owing to deficient irrigation by the 

 blood stream, on the other, a disturbance of the cerebral circulation 

 by suppression of the thyroid system. The constriction of the 

 trachea diminished the respiratory gas-exchanges, and indirectly 

 produced anaemia, leucocytosis, cretinism, coma ; the disturbance 

 of the cerebral circulation (according to Liebermeister's theory) 

 caused the convulsions, tachypnea, and tachycardia. 



After Schiffs publications (1884) these hypotheses, which, as 

 we shall see, were reared on an unstable basis, were abandoned 

 even by their authors. According to Schiff the grave symptoms 

 consequent on thyroidectomy are the direct consequences of 

 deficiency of thyroid function, i.e. of the internal secretion of 

 substances of unknown nature, which are of great importance in 

 the normal nutrition of the nervous system. When deprived of 

 these substances of thyroid origin the nervous system becomes 

 disordered in its functions, and gives rise to the phenomena of 

 tetany and cachexia thyreopriva. Schiff proved that the extirpa- 



