2 THE ROYAL SOCIETY OF CANADA 



which tannin occurs as an admixture with other solutes. With the 

 death of the cell the tannin may be transferred to surrounding sub- 

 stances, as occurs during the formation of cork (Drabble and Nieren- 

 stein, 1906), and in the cortex of tannin-bearing plants (e.g., Quercus- 

 densiflora, Lloyd in MS.), or it may not (Lloyd, 1916), as in 

 many fruits and seeds. During life, however, the tannin is strictly 

 impounded by the surface layer of protoplasm limiting the vacuole, 

 as shown long ago by Hugo de Vries (1885). What, then, is the 

 mechanism by which the tannin is thus confined? This question 

 demands more insistently to be answered than, I think, in the case of 

 innocuous or admittedly metabolically useful substances — -such as 

 sugar and so forth — -because of the fact that it is regarded by many 

 as a protoplasmic poison. It is true that some organisms can procure 

 the fermentation of tannic acid (Knudson, 1913, p. 165) and can 

 make use of it as food. But Cook, Taubenhaus and Wilson (1911, 

 1915) have shown that a large number of parasitic fungi are retarded 

 in growth by rather low concentrations of this substance: namely, 

 from 0.1 to 0.8 per cent. Saprophytic forms exhibit more resistance 

 — a conclusion supported by Knudson. However, precisely wherein 

 the supposed toxicity of tannin consists is somewhat more difficult 

 to answer. So far as I am aware, there have been few sustained 

 attempts to discover the facts. One suggestion which may be made 

 is that tannic acid has the power of inactivating enzymes (Katz, 

 1898; Knudson I.e. p. 191). If this should be generally true — as 

 seems not improbable — we should find in tannin a substance capable 

 of disturbing or inhibiting cell metabolism and thus indirectly throwing 

 the machinery out of gear. It will be seen that this could occur 

 without any direct action upon the protoplasm whatever. 



It has, however, been insistently argued (e.g., more recently by 

 de Dominicis, 1919) that the toxicity of tannin lies in its precipitating 

 power on albuminoids. It is easy to say that the tannin is confined 

 to the cell sap, but this statement not only assumes a semi-perme- 

 ability on the part of the protoplasm toward the tannin (an explana- 

 tion which might suffice if tannin were indeed non-toxic), but also 

 the impossibility of the tannin attacking the surface layer of living 

 protoplasm. Now, when we say that a substance is directly toxic we 

 mean that it can in some way attack the protoplasmic mechanism; 

 but the observed fact is that tannin is not capable of attacking the 

 living substance directly. I am aware that there is lacking evidence 

 to substantiate a general statement of this kind, but I may at any 

 rate generalize to an extent sufficient to say that when tannin occurs 

 in vacuoles and not external to the protoplast, it is incapable of 



