METABOLISM, NUTRITION AND DIETETICS 569 



It is not at present possible to deduce from such clinical and 

 experimental observations as those described any coherent 

 theory of the function of the pituitary. That there is some con- 

 nection between the normal action of the gland, and in particular 

 of its anterior lobe, and the normal growth and nutrition of the 

 skeleton is scarcely to be doubted. The fact that administration 

 of the dried gland substance to dogs causes an increased excretion 

 of calcium on a diet rich in calcium is a further indication of its 

 influence on the metabolism of bone (Malcolm). But so far is 

 the precise nature of this influence, if it exists, from being fully 

 understood, that authorities of repute are still divided on the 

 question whether the symptoms of acromegaly and gigantism 

 are due to atrophy or to hypertrophy of the active elements of 

 the gland, to loss of its internal secretion, or to its manufacture in 

 excessive amount. There is evidence that the colloid secretion 

 of the posterior lobe, probably formed by the epithelial cells of 

 the pars intermedia, passes through the nervous portion to 

 enter the infundibulum and the third ventricle of the brain, 

 where it breaks down in the cerebro-spinal fluid (Herring). And 

 it has been suggested that in virtue of the action of the hormones 

 (p. 375) in this secretion on the vascular system in general, and on 

 the renal cells and the renal circulation in particular, the posterior 

 lobe constitutes a mechanism for the control of the secretion of 

 urine. But this suggestion is still in the realm of hypothesis. 



Extracts of nervous tissue (sciatic nerve, white matter of brain, and 

 spinal cord, but especially grey matter of brain) cause, on injection 

 into the veins, a decided fall of arterial blood-pressure, which soon 

 passes off, and can be renewed by a fresh injection. The fall of 

 pressure is due to direct action upon the bloodvessels of a depressor 

 substance in the extracts, and not to the action of vaso-motor nerves. 

 It can be obtained after section of the vagi. 



.Extracts of muscular tissue also cause a distinct though transient 

 fall of pressure, but not so great a fall as in the case of extracts of 

 nervous tissue. Saline decoctions of other tissues (testis, kidney, 

 spleen, pancreas, liver, mucous membrane of stomach and intestine, 

 lung, and mammary gland) all produce a fall of blood-pressure 

 (Osborne and Vincent). The same is true of bone-marrow (Brown 

 and Guthrie ; Figs. 192, 193). It must be repeated that there is 

 no evidence that these depressor substances are specific internal 

 secretions in the same sense as adrenalin. 



Kidney. The experiments of Bradford, which seemed to indicate 

 that the kidney, in addition to its function as an excretory organ, 

 plays an important, and indeed indispensable, part in protein 

 metabolism, possibly by forming something of the nature of an 

 internal secretion, have not been confirmed. He stated that when 

 the half or two-thirds of one kidney and the whole of the other have 

 been removed from a dog by successive operations, death ensues, 

 although the quantity both of water and urea excreted by the frag- 

 ment of renal substance that remains is far above the normal. In 

 spite of the increased elimination of urea, that substance was said 



