PHYSIOLOGY OF NERVE 275 



the work of the electro-physiologist has received an entirely new 

 direction, namely, that of endeavouring to see how the laws of 

 solutions and electrolytes can be applied to living tissues. The 

 problem is by no means a simple one. The nature and composition 

 of the ions has to be determined. They might be either inorganic 

 electrolytes such as KC1, or more complex bodies such as occur in 

 the products of digestion. They might be present in the tissues 

 as such, or be formed by chemical action and then appear, and 

 their distribution may be controlled by semi- permeable membranes, 

 or by surfaces of separation which would act in a similar manner. 



Before considering the modern theories of nerve action it will 

 be convenient to note briefly the result of the micro-chemical work 

 of Macallum (" Mi M ) which has greatly influenced the theoretical 

 view of the subject in this country. 



Of these papers, two deal with the subjects with which we 

 are now concerned, namely, the determination of (1) potassium 

 and (2) chlorides in cells and nerve fibres. 



(1) To determine the potassium ( 51 ) fresh nerve fibres are placed 

 in a solution of cobalt sodium hexanitrite (Co.,Na 3 (No 2 ) 6 ) ; where 

 potassium is present, a precipitate is formed. According to 

 Gilbert ( 52 ) its formula is (Co(No 2 ) 2 3(K/Na)No 2 nH 2 0). The 

 excess of the reagent is washed away with ice-cold water, and 

 the precipitate blackened with ammonium sulphide. Macallum 

 found a precipitate in the medullary sheath where the neuro- 

 keratine network is supposed to exist, in Lanterman's imbrica- 

 tions, at the nodes of Ranvier, but not in the axis cylinder. Even 

 at the nodes of Ranvier, where the precipitate surrounds this 

 structure, the axis cylinder itself is free. 



(2) The distribution of the chlorides ( 53> 54 ) was investigated by 

 the addition to the tissues of T V normal AgNo 3 solution con- 

 taining 1'5 per cent. HNo 3 . The result is briefly the reverse 

 picture of the potassium. Chlorides are absent from the medullary 

 sheath. They are present all along the axis cylinder whenever 

 the reagent can penetrate, either at a node of Ranvier or an 

 injured spot. Lantermann's imbrications are an exception : K 

 and Cl are both found there. 



Taken as they stand, Macallum's researches would show that 

 in what is presumably the active part of the nerve, namely, the 

 axis cylinder, chlorides were present in greater amount than in either 

 the lymph outside or in the medullary sheath, while potassium was 



