340 Prof. J. 8. Macdonald. | Apr ize 
Apparently the only other conditions necessary to imitate nerve-function, and 
they at least are entirely reasonable conditions, are that the colloid solution 
should undergo some degree of a coagulative change when negatively charged, 
and that the negative anion of the contained inorganic salts should be 
relatively more rapid in its motion than the positive kation. 
Let us think of the strip as A, B,C, D, E. At A, the terminal point, let 
any agent be applied productive of a condition of degradation (tendency 
towards coagulation). The condition of degradation is at once the cause of a 
sudden rise in osmotic pressure due to the new freedom given to the inorganic 
salts. Instantaneously diffusion tends to take place into B, and the 
instantaneous result will be the conference of a negative charge upon this 
neighbouring portion, a positive charge upon the portion first affected. Point 
B is therefore now excited, and point A, originally excited, is brought back 
into a state of rest, and indeed, by reason of its positive charge, beyond that 
state into a condition of more perfect colloid solution than before. A has 
passed from a condition of excitation into a condition of inhibition, a condition 
however which it does not long retain; since backward diffusion from the 
newly excited point B reduces its positive charge, and brings it again to its 
original normal state. Point B at first made negative and thus excited is the 
seat of an increased osmotic pressure, and thus electrolytes are tending to 
move from it both backwards towards A, thereby annulling the temporarily 
positively charged state of A, and forwards to C, thereby conferring a negative 
charge upon C and producing in it the state of desolution and excitation. 
Each point in succession—point B may be taken as a typical instance—is 
first made negative, then positive, then returns to its state of rest. 
Considering the process in terms of the state of electrical potential, the 
forward movement of the negative charge is ensured, or rather its backward 
transmission is prevented, by the pursuing positive charge. Considered in 
terms of osmotic pressure the facts seem somewhat simpler, since it may or 
must be considered that the rise and fall of osmotic pressure respectively lag 
a definite time behind the appearance of the causes producing them. It is 
also conceivable that the rise, the release, is a more sudden phenomenon than 
the fall, the recall. The facts then arrange themselves in this manner. The 
rise of pressure in B occurs at a time when there is still a region of increased 
pressure behind it at A, but a region of normal low pressure in front of it at C. 
The tendency is therefore always forwards. Arranged in these terms the wave 
of the nervous impulse can be described as a double oscillation in the value of 
osmotic pressure, the front a rise, the trough a fall. 
In order to connect what has been already said of the nature of the “ pseudo- 
polarisation” of nerve, and this scheme of nerve-function, it may be well to 
