744 REPORT—1904. 
salt solution which has been freely exposed to air or oxygen. Under these con- 
ditions the response to stimulation of the surface consists of a succession of brief 
tetani, each lasting two or three hundredths of a second. The next step is to 
substitute salt solution which has been deprived of oxygen, and to observe that 
the reflex centre is gradually paralysed, as indicated by the fact that single 
tetani have taken the place of the serial responses, and that on renewing the 
supply of oxygen the former state of things is restored; and, finally, that these 
changes may be repeated over and over again with the same result. 
All of these facts come under the general statement that, while oxygen has 
no power of acting as a stimulus, it increases the excitability of the centre, 
enabling it when excited to discharge itself so completely that after the discharge 
it is wholly incapable of responding. It further shows that oxygen shortens the 
time required for restitution to the normal—reintegration following disintegra- 
tion—anabolism following catabolism so immediately that they may almost be 
considered as simultaneous. 
If we compare the behaviour of oxygen in the centre with its behaviour in the 
muscle, we shall find that they differ chiefly in one particular—namely, in their 
time-relations. In both cases oxygen acts as a predisposing, not as an exciting, 
cause of functional activity. In both cases a tertiwm guid is wanted—a liberating 
~ or letting-off mechanism; but in the muscle the functional cycle is accomplished 
in scarcely more than =; second, whereas in the centre the effect occupies a few 
hundredths of a second, and the preparation for it a much longer period. There 
is, therefore, no difficulty in understanding why the so-called refractory period 
can be so easily observed and measured in the centre (while in the muscle its 
presence can only be inferred), a circumstance which is helpful as affording an 
additional evidence of the anabolic action of oxygen; for it is easy to show that 
the period in question is shortened by supply of oxygen, protracted by its 
absence. 
We now come to the last point which I am anxious to submit to you—that 
of the relation of oxygen to the function of glands. I must begin by saying that 
it is in this part of our subject that the crux lies, for the investigation of the 
intimate metabolism of glands is beset with difficulties even greater than those of 
muscle and spinal cord. 
Mr. Barcroft, to whose admirable researches we shall have occasion to refer 
repeatedly to-day, found, as the result of his estimate of the oxygen and carbonic 
acid yielded by the blood circulating through the submaxillary gland under 
different conditions, that this gland takes from the blood much more oxygen when 
excited by the chorda tympani than when at rest, no such effect occurring when 
the excitation had been rendered ineffectual by the previous administration of 
atropine. These observations gave good reason for believing that oxygen pro- 
motes the action of the cells, but afforded no evidence that this action is attended 
by a corresponding discharge of carbon dioxide. Similarly, Professor Starling, 
whose experiments were made with Mr. Barcroft’s co-operation, found that when 
the pancreas is made to act by the injection of secretin, a similar want of relation 
presented itself between the quantity of oxygen taken in and of carbon dioxide 
discharged, Finally, the comparison which has been recently made by Dr. Brodie 
(who will, I hope, explain to us his very admirable method) of the state of activity 
of the kidneys with the state of rest points to the same conclusion as regards 
that organ. When diuresis was produced by the injection of urea, the clearest 
evidence was given of the increased demand for oxygen, the intake of which was 
very largely increased, but there was no indication that the ultimate products of 
oxidation found their way into the blood in quantities proportionate to the 
oxygen supplied. 
Taking these data as our point of departure, what can we infer from them as 
regards the resemblances and differences between the two processes we have been 
considering—viz., the functional activity of muscle and nerve centre on the one 
hand, that of gland on the other? The odviows contrasts which exist between 
secretion, muscular contraction, and reflex innervation need not be dwelt upon ; 
the one thing with which we have to do is the nature of the chemical processes 
