344 THE DUCTLESS GLANDS [CH. XXV. 



cells, which passes into the adjacent nervous substance, to be absorbed 

 by lymphatics which carry it to the cavity of the posterior lobe, and 

 so into the third ventricle of the brain. The existence of colloid 

 cysts in the pituitary closely resembling those of the thyroid has 

 led many observers to the conclusion that the function of the two 

 glands is similar, and that after removal of the thyroid the pituitary 

 may take on its work vicariously. After extirpation of the thyroid 

 gland, the cells of the pars intermedia do manifest increased activity, 

 and the colloid matter increases but this is all that can be said at 

 present in favour of such a view; the removal of the two organs 

 produces very different symptoms ; injection of extracts produces 

 different effects ; moreover, the pituitary contains no iodine, therefore 

 the colloid material is a different substance in the two cases. 



(3) The posterior lobe. This is connected to the floor of the third 

 ventricle, of which it forms a developmental outgrowth; in some 

 animals (cat) it remains hollow throughout life, in others (dog) the 

 neck alone remains hollow, and in most (including man) both body 

 and neck are solid, with traces of a cavity in the neck. Though 

 developed from the brain, it contains in the adult no nerve cells, but 

 consists mainly of neuroglia. It is surrounded and invaded by the 

 epithelium cells and colloid matter derived from the pars intermedia. 

 It plays the part of a brain gland in virtue of these epithelial cells. 

 What the use of the secretion into the third ventricle may be is far 

 from clear. P. T. Herring, to whom we owe many of the facts already 

 given, suggests that disturbances of the posterior lobe may be 

 responsible for the diabetic condition so frequently seen in cases of 

 acromegaly. Whether this is so or not, injections of aqueous 

 extracts : of the gland have pronounced physiological effects, and 

 these may be boiled without losing their activity. Although we do 

 not know the precise nature of the active substance (provisionally 

 called pituitrin) in the posterior lobe, we can at any rate say, there- 

 fore, that it is not protein. 



Intravenous injection of such extracts produces : 



1. A temporary rise of arterial blood-pressure ; this is not due to 

 the presence of adrenaline, for a second injection following the first 

 produces no such effect, whereas the rise of pressure produced by 

 adrenaline may be repeated time after time. The second and follow- 

 ing injections of pituitary extract, unless they occur at much pro- 

 longed intervals, produce only a slight fall of pressure, which is the 

 effect produced by most tissue extracts. The rise of pressure which 

 occurs at the first injection is, however, like that of adrenaline, pro- 

 duced mainly by constriction of peripheral arterioles. Slowing of the 

 heart may occasionally also be produced. Pituitrin causes also con- 

 traction of other forms of involuntary muscle, for instance the uterus. 



2. The extract has a specific effect on the kidney, and causes 



