14 THE EQUILIBRIUM OF COLLOID AND 



This type of union occurs par excellence, and in endless variety, 

 both as to number of substances so uniting and ranges of pressure 

 for union and disunion in the case of colloid with crystalloid, -and 

 in particular in living cells. Also in the building up of protein 

 and bioplasm, there occur endless varieties in the modes of group- 

 ing of the constituent radicles, which give rise to the selective 

 affinities of the cells, and cause one cell to enter into selective 

 union with one constituent of the plasma at a different level of 

 pressure (concentration) from another, or to possess affinities of such 

 a difference in order, that a substance is taken up with avidity 

 by one cell and apparently refused altogether by another. The 

 groups in cell and in substance entering into union with it are 

 often so delicately arranged that the change of a single radicle 

 alters the result entirely ; as, for example, in the action of strychnine 

 at very low pressure upon the nerve cells of the central nervous 

 system changing at once and practically disappearing when a 

 methyl group is added to the strychnine molecule, or the more 

 slightly poisonous action of piperidine passing into the most virulent 

 action of coniine, when a propyl group (C 3 H 7 ), in itself a harmless 

 enough constituent, replaces one of the hydrogen atoms as a side 

 chain. 



We may now pass to the consideration of the evidence that the 

 various organic and inorganic constituents in tissue cells and plasma 

 are held in loose union by the bioplasm or proteins. 



First, in regard to the carbohydrate material present in the 

 blood, it has been shown that if a stream of carbon-dioxide be 

 passed through a sample of blood, or if an anaesthetic such as 

 chloroform or ether be added to it, and then it be subjected to 

 dialysis, the amount of sugar passing into the dialysate is con- 

 siderably increased, above the amount in the case of untreated 

 blood. It was at first supposed that this increased amount of 

 sugar came from the blood corpuscles, but more recent work has 

 demonstrated that there is practically no sugar present in the 

 corpuscles, and further a similar and equal increment in amount of 

 sugar dialysing out can be obtained when clear serum is used for 

 the experiment instead of whipped blood. If now a stream of air 

 be passed through the serum in order to remove the carbon-dioxide 

 or anaesthetic before the serum is subjected to dialysis, it is found 

 that the yield of sugar in the dialysate has passed back again to 

 the normal amount. 



