84 INTIMATE ASSOCIATIONS OF IXORGAXIC lOXS 



paralysis and anaesthesia and a low blood-pressure; it can he 

 rapidlv antagonised by either the chloride or the acetate of 

 calcium, which revives the respiration in a surprisingly short 

 time, but not by barium. It would seem as though in a non- 

 vital union, barium and calcium were interchangeable, but not 

 so in vital chemical complexes. Thus, the influence of mag- 

 nesium is the same as that of calcium in inhibiting the 

 spontaneous twitching of muscles immersed in solutions of 

 sodium or lithium and in antagonising the contraction of 

 skeletal muscle brought about by potassium salts ; but in regard 

 to its action on the heart, magTiesium stands quite apart from 

 calcium, barium and strontium, and is totally unable to replace 

 these in the cardio-inhibitory mechanism or at the skeletal 

 neuro-muscular j unction. 



And this is to a large extent comprehensible, for chem- 

 ically, such substances as caseinogen, blood-germent, albumin, 

 etc., and not to be taken as the equivalents of living matter, com- 

 plicated as they are. The metabolism of calcium is full of 

 lessons for us ; one result of its presence in blood is to confer a 

 certain degree of viscosity on that fluid. If there is too little 

 viscosity, there is a tendency for the blood-plasma to exude too 

 freely through the capillary wall so that an oedema or urticaria 

 may be produced which is rapidly removed by the administra- 

 tion of a soluble salt of calcium — the chloride or lactate. It 

 is j)ossible that the tissues of haemophiles may suffer from a 

 congenital inability to absorb or incorporate calcium. But 

 indeed the whole doctrine of ionisation has been of great service 

 in biology: for this may be taken to be the converse oi the 

 chemical condition of union of ions or atoms with the protein 

 or living matter. Thus in the simple case of action of acids 

 on living tissues, it is found that e. g. HCl is far more destruc- 

 tive to enzymes (except pepsin) than is acetic, the only satis- 

 factory explanation of this being that HCl is far more per- 

 fectly ionised that acetic, not more than 3^ of which is ionised. 

 Since in regard to the effects of different acids, it is highly 



