58 LIBBIE H. HYMAN 



susceptibility gradient is a gradient in metabolic rate, that is, the 

 regions most susceptible to poisons are those where the metabolic 

 reactions occur with the highest speed. The fact that a great 

 variety of substances will give a death gradient shows clearly that 

 their action cannot be specific but that all affect the same general 

 fundamental process in the protoplasm. And this process is that 

 complex we designate as metabolism since all factors which are 

 known to modify the metabolic rate also modify the suscepti- 

 bility to these substances and in the same direction. This rela- 

 tion between susceptibility and metabolism is further confirmed 

 by direct determinations of carbon dioxide output in a Tashiro 

 biometer or by an indicator (as the phenolsulphonephthalein 

 colorimetric method of Haas, '16); those parts of an organism 

 most susceptible to cyanide and other substances give off the 

 most carbon-dioxide, i.e., they are carrying on metabolic proc- 

 esses at a higher level. Similarly the precipitation of indo- 

 pheno ( l is a direct measure of oxygen consumption, and is greatest 

 in those regions which are most susceptible. Some of the sus- 

 ceptibility reagents may affect metabolism directly — potassium 

 cyanide almost certainly does so (cf. Hyman, '16 b) 5 — while 

 others may act indirectly. The existence of axial electric cur- 

 rents in organisms confirms our general conclusion since bio- 

 electric currents are invariably associated with increased func- 

 tional activity, as nerve conduction, muscle contraction, gland 

 secretion, etc. Furthermore the region of increased activity is 

 always electro-negative (externally) to non-active regions. If, 

 then, the anterior or apical end of organisms is more active 

 metabolically than posterior levels, it should be electro-negative 

 to them, as is exactly the case. 



6 A consideration of the structure of potassium cyanide suggests why it has 

 such a powerful effect on protoplasm. Potassium cyanide is not really a cya- 

 nide, but an isocyanide, that is, its structural formula is K — N = C. It there- 

 fore contains bivalent carbon, one of the most reactive atoms known to chem- 

 istry, since it has two unoccupied valences which unite with the greatest avidity 

 with many atoms and radicals, or in lieu of those with other molecules of cya- 

 nide. Bivalent carbon unites with oxygen with extreme readiness, and potas- 

 sium cyanide is in fact one of the most powerful reducing agents known; hence, 

 its effectiveness in depressing and inhibiting oxidations in protoplasm and 

 elsewhere. 



