APPENDIX 237 



chloride we may consider that the number of ions is double the number of 

 molecules of the salt present. 



The ions liberated by the act of dissociation are, as we have seen, charged 

 with electricity, and when an electrical current is led into such a solution 

 it is conducted through the solution by the movement of the ions. Sub- 

 stances which exhibit the property of dissociation are known as electrolytes. 



The conception of electrolytes, which we owe to Arrhenius, is extremely 

 important in view of the question of osmotic pressure which we shall be con- 

 sidering immediately ; because the act of dissociation increases the number 

 of particles moving in the solution and so increases the osmotic pressure, for 

 in this relation the ion plays the same part as a molecule. 



The liquids of the body contain electrolytes in solution, and it is owing 

 to this fact that they are able to conduct electrical currents. 



Another physiological aspect of the subject is seen in a study of the 

 action of mineral salts in solution on living organisms and parts of organisms. 

 Many years ago Einger showed that contractile tissues (heart, cilia, &c.) 

 continue to manifest their activity in certain saline solutions. Indeed, as 

 Howell puts it, the cause of such rhythmical action is the presence of these 

 inorganic substances in the blood or lymph which usually bathes them. In 

 the case of the heart, the sinus, or venous end of the heart, is peculiarly 

 susceptible to the stimulus of the inorganic salts, and the rhythmical 

 peristaltic waves so started travel thence over the rest of the heart muscle. 



Loeb and his fellow workers have confirmed these statements, but interpret 

 them now as ionic action. Contractile tissues will not contract in pure 

 solutions of non-electrolytes (like sugar, urea, albumen). But different con- 

 tractile tissues differ in the nature of the ions which are most favourable 

 stimuli. Thus cardiac muscle, cilia, amoeboid movement, karyokinesis, cell 

 division are all alike in requiring a proper adjustment of ions in their sur- 

 roundings if they are to continue to act, but the proportions must be different 

 in individual cases. Ions affecting the rhythmical contractions may be 

 divided into three classes : (1) Those which produce such contractions ; of 

 these the most efficacious is Na. (2) Those which retard rhythmical con- 

 tractions ; for instance, Ca and K. (3) Those which act catalytically, that 

 is, they accelerate the action of Na, though they do not themselves produce 

 rhythmical contractions directly : for instance, H and OH. In spite of the 

 antagonistic effect of Ca, a certain amount of it must be present if con- 

 tractions are to continue for any length of time. Ions produce rhythmical 

 contraction only because they affect either the physical condition of the 

 colloidal substances (protein, &c.) in protoplasm, or the rapidity of chemical 

 processes. 



Loeb has even gone so far as to consider that the process of fertilisation 

 is mainly ionic action. He denies that the nuclein in the head of the sperma- 

 tozoon is essential, but asserts that all the spermatozoon does is to act as the 

 stimulus in the due adjustment of the proportions of the surrounding ions. 

 He supports this view by numerous experiments on ova, in which, without 

 the presence of spermatozoa, he has produced larvae (generally imperfect 

 ones, it is true) by merely altering the saline constituents of the fluid that 

 bathes them. Whether such a notion will stand the test of further verifica- 



