COLLOIDS IN PROTOPLASM 



to differ very clearly. But now we know that 

 Natura non facit sallus, not even in colloid and 

 crystalloid matter. The chemistry of proteins 

 showed that typical colloids, for instance, egg- 

 albumin, are step by step transferred into typically 

 soluble substances when these proteins are split 

 up into the products of digestion by the working of 

 digestive ferments. The first products of de- 

 composition, the proteoses, show the typical 

 colloid properties, only slightly less marked than 

 the original protein. The peptones, the next 

 product of decomposition, are not crystallisable, 

 but are distinctly different from typical colloids. 

 Their molecular weight is certainly less than 1000, 

 and they are distinctly electrolytes. Another 

 example of an intermediate state between colloids 

 and crystalloids is demonstrated in soap solutions. 

 Both peptones and soaps are important and widely 

 spread constituents of cell-plasma. Such sub- 

 stances forming transitions from colloids to 

 crystalloids may be called Semicolloids. On the 

 other hand, we have to confess that we cannot 

 draw a sharp line of distinction between liquids 

 containing solid particles suspended and colloidal 

 solutions in which only molecules of a large size 

 can be present. These facts are of the greatest 

 importance for Biology. 



The chemists Linder and Picton were able to 

 show how suspensions of the yellow sulphide of 

 arsenic are obtainable in particles of all sizes. 

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