PROPAGATION OF PHYSIOLOGICAL CHANGE 497 



solution within the core. On immersing fibres in solutions 

 of different concentrations attention is at once drawn to 

 the precipitations and re-entrance into a state of solution of 

 the colloid material present. Such variations have also been 

 observed by Hober in nerve-fibres treated with solutions of 

 electrolytes, and have been inferred as of probable occurrence by 

 Matthews, Greeley, Loeb, Lillie, and others. Nor is there any 

 need to vary the character or concentration of the surrounding 

 solution to observe these effects, since a distribution of varied 

 states of colloidal solution is discoverable in nerve-fibres 

 immersed in the solution usually first made use of, such as 

 " normal saline " or " Ringer," solutions somewhere about 

 the concentration of a decinormal solution. The states thus 

 observed have a definite relation to injury and to the injury 

 current which arises from it. At the cut end, the source of 

 this current, there is some precipitation of colloid matter from 

 solution ; this portion is limited by a stretch of limpid solution 

 and this is again succeeded as we reach kathodal points, where 

 the current is leaving the nerve-fibre to enter the surrounding 

 solutions, by successive tracts showing greater and greater 

 degrees of precipitation. 



But this is an observation pregnant with suggestion, since 

 the conditions present at " kathodal points " are as of great an 

 interest as those present at the injured region. If there were 

 hesitancy in postulating something of the nature of excitation 

 as influencing the conditions due to injury, there can be none in 

 case of the kathode. The institution of the kathodal condition 

 has been shown to be the cause of that excitation which follows 

 the admission of an electrical current into a nerve. During the 

 closure of the current the whole region of the kathode is in a 

 state of increased excitability. It is significant, therefore, that 

 at such points there is again a visible alteration in the core. The 

 importance of this fact is enhanced by microchemical proof that 

 in this district also there is present a solution of a potassium 

 salt of much greater concentration than that to be found in any 

 other part of the nerve-fibre except the region of injury. There 

 is therefore some basis for the statement, that at every excited 

 point there is a coarser aggregation of colloid material, accompanied 

 by the appearance of a Jiezv quantity of potassium salt in a state of 

 simple aqueous solution. 



Apparently, therefore, the facts discoverable under these 



