330 PROPERTIES OF THE COLLOIDAL CONSTITUENTS 



It is to the protein compounds in the main that we must look, therefore, 

 for the origin of the selective ability of tissues. 



Many of the Heavy Metal Salts, such as those of mercury, silver, 

 lead or copper are highly toxic for living organisms in extraordinarily 

 high dilutions. Even water distilled from a metallic still, or collected 

 in a metallic condenser may be extremely toxic to many forms of life. 

 This phenomenon appeared so impressive to the botanist Nageli that 

 he invented a special phrase " oligodynamic action" to describe it. 



The phenomenon is not so surprising as it might appear, however, 

 when we recollect that heavy metal ions are protein precipitants and 

 especially tend to form insoluble and non-dissociated compounds 

 with proteins. The effect of this is to reduce the concentration of 

 heavy metal ions in any region containing protein, and if the protein 

 is surrounded by a medium which still contains free metal ions these 

 will diffuse in to take the place of those precipitated or rendered non- 

 dissociable. These in turn will be removed from the solution and so 

 the process will go on until, although the original concentration of metal 

 ions in the external medium may have been very small, in the end the 

 concentration of combined metal in a cell may be considerably greater 

 and quite sufficient to constitute a lethal dosage. As W. A. Osborne 

 has shown, this sequence of events may be directly observed by plac- 

 ing a protein solution inside a parchment-dialyzer and immersing the 

 dialyzer in an exceedingly dilute solution of mercuric chloride. The 

 mercury quickly attains a higher concentration within the dialyzer 

 than without, because as rapidly as it enters it is bound, and the 

 osmotic gradient remains positive from the medium without to the 

 protein solution within the dialyzer. 



THE BIOLOGICAL INDIVIDUALITY OF TISSUES AND TISSUE- 

 FLUIDS. 



In discussing the various compounds which the Proteins are capable 

 of forming we had occasion in Chapter VIII to dwell upon the existence 

 and the properties of the compounds of proteins with other proteins 

 and especially upon the demonstration afforded by the investigations 

 of Hardy, that the Serum-globulin which is separable from blood- 

 serum by dilution and acidification is not present as such in the 

 untreated serum but in the form of a complex, probably arising out of 

 the union of several protein molecules. 



The presence of these protein complexes in the tissues and tissue- 

 fluids affords a simple and readily intelligible explanation of what 

 would otherwise constitute an exceedingly puzzling fact, namely, the 

 Biological Individuality of the various tissues and tissue-fluids. The 

 individual proteins which are found in the tissue-fluids of tolerably 

 nearly related animals, for example in the tissue-fluids of the various 

 species of mammalia, appear, on analysis, to be either identical or 



