592 THE POSTERIOR PITUITARY AND THE NERVOUS SYSTEM. 



the presence of so many neuroglia-cells at the apex i.e., where 

 the posterior pituitary meets the infundibulum indicates that 

 the neurons which they supply are the seat of marked func- 

 tional activity. 



The salient feature brought to light by Howell's experi- 

 ments, however, is the identity of the posterior lobe as only one 

 containing an active agency. This obviously harmonizes with 

 our views, since, as we have seen, the anterior lobe is, to a 

 certain degree, passive in that it is stimulated to an inordinate 

 degree only when toxics are present in the blood, while its nor- 

 mal activity is sustained by the secretion of the thyroid gland. 

 Though the purpose of both organs is similar, therefore, 

 the conversion of chemical energy into nervous energy, the 

 manner in which this is done is not similar. Indeed, in the 

 posterior lobe, the exciting agency is, as just stated, precisely 

 as it is in any organ: i.e., oxygen. The posterior pituitary 

 must, therefore, become physiologically active through the same 

 chemico-physical process that prevails elsewhere in the or- 

 ganism. 



Indeed, we have seen that the posterior lobe is, in reality, 

 but an aggregate of neurons and a precious aggregate it must 

 be, ensconced, as it is, in a bony cradle and resting on a pillow 

 of blood, to preserve it against shocks or traumatisms! That, 

 like all neurons, this aggregate depends mainly upon a phos- 

 phorus-containing ground-substance has been shown. We will 

 recall, in this connection, the labors of de Cyon, 61 who, in the 

 course of a large number of experiments, observed that: "1. 

 Any, even slight, pressure upon the hypophysis (i.e., both or- 

 gans) immediately gives rise to a sudden variation of blood- 

 pressure and to a notable reduction in the beats of the heart, 

 the strength of which is at the same time considerably in- 

 creased. 2. Electrical stimulation of the hypophysis, even with 

 extremely weak currents, produces exactly the same phenom- 

 ena as does mechanical pressure, but in a much more intense 

 manner. 3. Extract of hypophysis, injected into the veins 

 of an animal, produces upon the heart and upon blood-pressure 

 effects that are analogous to those caused by electrical and 



81 De Cyon: Archives de Physiologie, July, 1898. 



