SECRETION. 451 



vagi or by way of the spinal cord and splanchnic nerves. That it is not by 

 way of the vagi is shown by the fact that the glycosuria established by the 

 puncture does not disappear when they are divided; that it is by way of the 

 spinal cord, as far at least as the first dorsal nerve, and subsequently the 

 splanchnic nerves, is indicated by the fact that a cross-section of the spinal 

 cord above this level, destruction of the upper three dorsal roots as well as 

 division of the spanchnic nerves prevents the development of the glycosuria 

 which follows puncture of the medulla. Though stimulation of the upper 

 dorsal (pre-ganglionic) nerve-fibers gives rise to glycosuria, yet, contrary to 

 expectation, stimulation of the splanchnic (post-ganglionic) nerve-fibers 

 does not have the same effect. This may be due, however, to changes in 

 the relation of the capillary blood-vessels to the liver cells or to the character 

 of the stimulus employed. 



A further question arises as to whether the nerve impulses which pass 

 from the diabetic center to the liver are vaso-motor in character, exerting 

 their effect on the blood-vessels, or whether they are secretor in character 

 and exerting their effect on the liver cells. Bernard was of the opinion that 

 they are vaso-motor in character and that the diabetic area was a part of the 

 general vaso-motor center. More recent investigators are of the opinion 

 that they are secretor in character, for the reason that whether the blood- 

 pressure rises from a stimulation of the central end of the divided vagus, or 

 falls from a stimulation of the depressor nerve, in each instance there follows 

 a glycosuria. 



If the production of sugar in the liver is a reflex act as Bernard supposed, 

 taking place through a mechanism consisting of an afferent pathway, the 

 vagus nerve, and an efferent pathway consisting of the spinal cord and 

 splanchnic nerves, the question arises as to the seat of action of the stimulus. 

 This Bernard located in the lungs, for the reason that though division of the 

 vagus in the neck checks the production of the sugar, division below the 

 origin of the pulmonary branches had no such effect. 



Muscle Glycogen. Glycogen is also found in muscles and to some 

 extent in the placenta, and embryonic tissues generally. Chemic analysis 

 has shown that muscles contain from 0.5 per cent, to i per cent, and as 

 these organs amount to about 40 per cent. (28 kgm.) of weight of the body, 

 70 kgm., they generally contain from 140 to 280 grams of glycogen. Inas- 

 much as chemic analysis has failed to demonstrate the presence of glycogen 

 in the blood, the inference is that it arises in the muscle-cell in a manner 

 similar to that observed in the liver-cell, viz., by a transformation, through 

 hydration, of the sugar of the blood. By reason of this fact it may be said 

 that the muscle also possesses a glycogenic function. If it is a fact that of 

 the sugar absorbed only from 12 to 20 per cent, is temporarily arrested by the 

 liver, the remainder passing on into the blood of the general circulation, it is 

 readily conceivable that the storage of the sugar under the form of glycogen 

 by the muscle-cells is necessary not only for the activity of the muscle itself, 

 but as a means of preventing an abnormal percentage of sugar in the 

 circulating blood. It is generally admitted that though the glycogen is the 

 source of the energy expended by the muscle, it cannot be disrupted and 

 oxidized as such, but that it must first be transformed into sugar (glucose) ; 

 and for this purpose the assumption is made that a special enzyme is present 



