4 THE EQUILIBRIUM OF COLLOID AND 



must be increased to nearly a whole atmosphere of pure oxygen 

 by bubbling oxygen gas through the Ringer's saline heated to 

 mammalian body temperature in a flask attached to the perfusion 

 cannula, before a normal heart beat can be obtained. This in- 

 creased oxygen pressure supplies the place of the red blood cor- 

 puscles which in the body are able to carry a sufficiency of oxygen 

 at the lower pressure of oxygen present in the lungs. Also, in 

 the case of the mammalian heart for a prolonged experiment, it 

 is well, as recommended by Locke, to add dextrose to the Ringer's 

 solution to prevent exhaustion of organic combustible material 

 which occurs earlier in the case of mammalian muscle on account 

 of the greater expenditure of energy which here occurs at each 

 heart beat. 



Before leaving the classical example of cardiac muscle for 

 more general considerations, the similar action of anaesthetics may 

 be mentioned as an example of the relationship of drugs to the 

 cell-protoplasm. 



The conditions which govern the action of chloroform upon 

 the isolated mammalian heart have been beautifully demonstrated 

 by Sherrington and Sowton. These observers have shown that 

 at a fairly definite concentration of chloroform in the circulating 

 saline the heart beat becomes affected, and if this concentration 

 be passed the beat is stopped. If now the chloroform be cut off 

 and pure Ringer's solution be perfused instead of it, after a short 

 time sufficient to reduce the osmotic pressure of the chloroform 

 in the cardiac cells below a definite limit, the heart recommences 

 its beating, and soon becomes normal once more. The conditions 

 of action here are obviously the same as in the case of the in- 

 organic ions above mentioned, except that the result is reversed, 

 and whereas in the case of the inorganic ions a certain pressure 

 or concentration of ions was essential in order to keep the heart 

 functionating normally, here a certain pressure of ana3sthetic is 

 required to still its activities. As soon as the osmotic pressure of 

 the anaesthetic passes below a certain limit, the cells cease to be 

 anaesthetised. In other words, some grouping in the protoplasm 

 is free from the anaesthetising influence and open to continue other 

 chemical interchanges which give rise to its activity. Within 

 certain well-marked limits there is a certain reduced activity or 

 anaesthesia. On one side of this is free activity or absence of 

 anaesthesia ; on the other side there is complete anchoring of proto- 



