422 PRINCIPLES OF GENERAL PHYSIOLOGY 



water in the tank, and this in itself increases the outflow owing to the rise of 

 driving pressure. That is, increase of anabolisni, or rather the anabolic state of 

 the cell, increases catabolism, instead of decreasing it. We arrive at the same 

 result if we regard the process from the point of view of a reversible chemical 

 reaction. Increase of the mass of a material undergoing decomposition will 

 increase the amount of decomposition taking place in a given time. Indeed, one 

 cannot imagine a process in which increase of activity in one direction necessarily 

 involves decrease in the opposite one. As Forbes puts it, to assume that increase 

 of anabolisni necessarily implies decrease of catabolism, is to suppose that 

 increasing a man's salary ensures decrease of his expenditure. To return to the 

 tank, suppose that we reduce catabolism by narrowing the outlet, the level will 

 rise, and consequently the inflow will diminish. That is, so far as the tank itself 

 is concerned, the effect is the same as increasing anabolisni. If we increase the 

 outflow, we increase also the inflow. Indeed it appears as if Hering had fixed his 

 attention too exclusively on the static condition of the protoplasm of the cell, 

 which is certainly increased in amount by increasing anabolisni. But if we look 

 at the really important dynamic condition, there seems no doubt that increase of 

 anabolisni must also increase catabolism. 



There are, on the contrary, certain facts which must not be overlooked, which 

 appear to support this nutrition theory. If we turn to Fig. 113 (page 405) we 

 notice that after the inhibitory pause, the first few beats are larger than those 

 preceding the pause. It looks as if inhibition had, by increasing the contractile 

 material, raised the functional capacity of the tissue. The question is whether 

 this result is any greater than it would be after an equal rest produced in any 

 other way. A further consequence of the anabolic theory would appear to be 

 that the longer the rest, the greater the subsequent improvement. In Fig. 113 

 there is no relation between the two, and in Fig. 109 of Gaskell's article (1900, 

 p. 205) the first beats are smaller than normal. We may have, in fact, after 

 an inhibitory pause, the same condition as that shown by the " staircase " 

 phenomenon of a ventricle which has been at rest for some time, owing to 

 separation from the sinus. 



In the case of inhibitory reflexes to skeletal muscles, we frequently find a 

 subsequent augmentation of contraction, called by Sherrington " successive 

 induction " or " rebound contraction." The effect of inhibition of various durations 

 on this phenomenon has been studied by Forbes (1912, 1) and several important 

 facts relating to inhibition in nerve centres have been brought out. There are 

 two different phenomena concerned : the " rebound " after a brief inhibition, 

 a contraction which is too great to be explained by mere " damming up " of 

 " energy " ; and, secondly, the effect of a prolonged period of inhibition on a 

 subsequent excitation. It is shown that this latter effect depends on the strength 

 of the stimulus of the inhibitory nerve. If moderate, it has a favouring effect, 

 if strong, a depressing one ; so that there is a " critical value " between the two, 

 where no effect* results. An important fact is that this critical value is lowered 

 if the inhibitory stimulus is accompanied by an excitatory one. This result 

 indicates that the two kinds of synapse have a more or less close relation to one 

 another and will be found to have a bearing on the theory of inhibition. In the 

 depressor reflex on the blood pressure in the rabbit, I found (1893, p. 320) that 

 the state of the centre was the same before and after sixteen minutes' continuous 

 stimulation of the inhibitory nerve, during which time the centre was in a state of 

 inhibition, as shown by the unchanged fall of blood pressure. 



The part played by fatigue is of interest. If a nerve which causes an excitatory 

 reflex be stimulated, fatigue is produced after a certain time. Now it might be 

 thought that, if an inhibitory nerve be stimulated at the same time, fatigue would 

 be diminished. Forbes shows that the contrary is the case. Fatigue comes on 

 earlier (p. 170). Further, an inhibitory reflex itself is capable of fatigue (p. 179); 

 or rather, a prolonged inhibition, with fairly strong stimulation, diminishes the 

 inhibitory effect of a test stimulus made immediately afterwards. To interpret 

 this result, we must bear in mind some facts as to the seat of fatigue. As 

 Sherrington has pointed out (1906, pp. 103-105), the seat both of excitation and of 



