PROCEEDIXGS OF SKCTIOX D. 493 



in it, changes whicli culminate in death. Possibly this is because they 

 cannot be replaced from their combination with proteins, inasmuch as 

 the combination is insoluble, and is therefore carried in part or wholly 

 out of the sphere of chemical action. The actions of some of the salts 

 of the heavy metals can, however, be partly or wholly counteracted by a 

 great excess of other salts (36). 



It is a curious fact, howev(;r, and of great theoretical interest, that 

 even the salts of the alkalies and alkaline earths, which do not, as a rule, 

 form insoluble compounds with proteins, nevertheless stand in a double 

 relation towards tissues. On the one hand they induce properties which 

 are readily modified or reversed by other salts; on the other hand, in 

 some instances, they undoubtedly form compounds of a more stable type, 

 and not nearly so readily converted by substitution into other compounds. 

 I refer to the well-known power possessed by certain living tissues of 

 " selecting " or storing up certain salts in a concentration much greater 

 than the medium in which they live. For example, the muscles of 

 animals contain a very much higher percentage of potassium than the 

 blood which bathes them. Obviously, if the potassium existed in the 

 muscle in a dissociable, readily replaceable form, it would speedily 

 diffuse out into the blood, and its place would be taken by some other 

 substance, probably sodium. That this does not occur indicates that the 

 potassium, is partly and temporarily present in the form of an irreversible 

 compound — irrever.sible because the potassium ion in dissociation is not 

 split off as such. We are therefore in possession of the suggestive fact 

 that, whereas in the type of alkali or alkaline earth ion-proteins usually 

 formed, the alkali or alkaline earth ion is readily dissociated as such ; 

 yet another type of combination exists, possibly with the same molecule 

 in which the alkali or alkaline earth ion is not dissociated as such, but is 

 bound up in a non-diffusible complex. 



Secondly, as regards the chemical affinities of the ion-proteids when 

 formed. In a paper published in the " Transactions of the Royal Society 

 of South Australia." early in 1905, and in subsequent papers (37), I have 

 pointed ovit that the relative velocities of migration of the ions in a 

 medium in which a tissue is bathed probably play an important part in 

 determining the kind and proportions of the ion-proteids formed in the 

 tissue. We have seen that the mass of a given ion present in a solution 

 bathing a tissue determines to a large extent the amount of the compound 

 with that ion which will be formed in the tissue. When magnesium ions 

 are in excess, for example, the magnesium compound will be the one 

 chiefly formed ; when calcium ions are in excess the calcium compound 

 will be the one chiefly formed, and so on. Now a salt, before it can 

 combine with a constituent of a tissue, has to diffuse into the tissue, and 

 both ions of a salt do not diffuse equally rapidly, while m acids and 

 alkalies the hydrogen and hydroxyl ions respectively have very much 

 higher velocities of migration, that is, diffuse more rapidly than the other 

 ions in the solution. It is this principle which is made use of in 

 Lipman's capillary electrometer (38). Here mercury and a dilute 

 sulphuric acid solution are brought into contact with a capillary glass 

 tube. The hydrogen ions of the sulphuric acid diffuse into the mercury 

 much more rapidly than the SO4 ions. Now hydrogen ions carry a posi- 

 tive charge, and SO4 ions carry a negative charge; hence, since an excess 

 of hydrogen ions enters the mercury, an excess of SO4 ions are left behind 



