304 THE EQUILIBKIUM OF COLLOID AND 



upon that bridge or interval of partial combination between proto- 

 plasm and anaesthetic, where there is just sufficient combination 

 between the two to produce the stilling of activity which gives 

 the absence of pain, but not sufficient to cause complete stilling 

 of activity nor that degree of combination which cannot become 

 reversible and dissociate off when the pressure of anaesthetic is 

 lowered by discontinuing the administration and allowing the 

 process of respiration to lower the pressure of anaesthetic in the 

 nerve cells. 



There is fortunately here, as in the case of all drugs, a degree 

 of selective absorption by different types of cells, and the cells of 

 the higher nerve centres are affected before other lower centres, 

 and these again before cardiac and other forms of muscle cells. 

 It is on this selective effect that all the benefits of anaesthesia as 

 an accessory of surgery depend, for if the heart, for example, were 

 affected at the same level of concentration of the anaesthetic as the 

 higher nerve cells, anaesthesia would become impossible. Precisely 

 at the same moment as anaesthesia set in the heart would stop 

 beating. 



In general terms it may be stated that the actions of all specific 

 drugs depend upon this delicate selective action between the cells 

 of different tissues, or parasitic cells, and the drugs. The problem 

 of practical therapeutics is to find a drug or chemical combination 

 which by its peculiar chemical conformation is capable of under- 

 going adsorption at a lower pressure by a specific type of cell 

 protoplasm. This subject will be treated more in detail later on 

 when we have considered the general conditions governing the 

 relationships of the protoplasm to crystalloids, and to the other 

 substances with which it is brought in contact in the cell either 

 naturally, or as a result of disease, or in the treatment of disease. 



We may now turn to a consideration of the general chemical 

 nature of protoplasm in so far as this bears upon its power of 

 adsorbing or combining with inorganic ions or other substances 

 which may be present in common with it in the living cell. 



The most essential and as it were the central constituents in 

 building up the excessively complex physicochemical aggregation 

 which we term protoplasm or bioplasm are the protein bodies. 

 By means of the proteins, the fats and carbohydrates are knitted 

 together with the variously constituted proteins themselves and 

 with the ions of the inorganic salts to form a united system. The 



