222 PRINCIPLES OF GENERAL PHYSIOLOGY 



From the work of Raulin it appeared also that iron in traces had a great effect 

 on the normal production of the fructification (conidia) of the mould. Bertrand 

 (1912), having been able to prepare solutions in a great state of purity, found that, 

 although iron and zinc might both be present, there were no conidia formed unless 

 manganese was also present. If any one of these three elements is wanting, or 

 present in too small a quantity, complete normal growth is impossible. But 

 whereas vigorous growth of mycelium takes place with iron and zinc alone, no 

 conidia are formed in the absence of manganese. 



OLIGODYNAMIC ACTION 



The opposite phenomenon to the favourable action by traces of zinc on 

 Aspergillus are to be found in the toxic action of certain metals, especially copper, 

 more particularly to the higher organisms. 



In a posthumous paper by Nageli (1893), some very important results are 

 described in relation to this question. It was noticed that ordinary distilled 

 water was rapidly fatal to Spirogyra, just as Ringer and Phear at a later date 

 (1895) found that it was to tadpoles. 



Nageli discovered that the toxic action was due to the presence of minute 

 traces of compounds of various heavy metals in the water. Tap water, which 

 originally did not show this property, became poisonous after being in contact 

 with metallic copper, mercury, lead, tin, iron, or silver. It was also found that 

 the addition of various insoluble solids, such as paper, wool, paraffin, or of certain 

 colloids, such as gum or gelatine, deprived the water so treated of its toxic 

 character. From what has been said in previous chapters of this book, when 

 dealing with the colloidal state and the phenomena of adsorption, the explanation 

 of this neutralising power of surfaces will be obvious. The toxic metal is present 

 either as hydroxide or carbonate in the colloidal state ; this, as an electro-positive 

 colloid, will be strongly adsorbed by electro-negative surfaces, such as those used 

 by Nageli. The fact noticed by Ringer (1886, p. 292) that calcium phosphate is 

 more effective in neutralising the toxic properties of distilled water than calcium 

 chloride is, is easily explained by the greater precipitating action of the trivalent 

 PO 4 '" ion on an electro-positive colloid than that of the univalent Cl' ion. 



Nageli estimated the amount of copper present in 1 2 litres of distilled water, 

 which had been for four days in contact with 12 two-pfennig pieces. It 

 contained one part in seventy-seven millions. This water was powerfully toxic to 

 Spirogyra, killing it in one minute. On account of the very small quantity of 

 copper in the water, Niigeli gave the name of " oliyodynamic " to .the action in 

 question. 



Locke (1895), in repeating these experiments, found that, of the various 

 metals tested, copper was by far the most toxic. A strip of bright copper, 4 "5 

 by 1*5 cm. in dimensions, placed for twenty hours in 200 c c. of distilled 

 water, made the water toxic to tadpoles and to the river worm, Tubifex. Brass 

 had the same effect as copper, but zinc, although toxic, was not so powerfully 

 active, while tin appeared to be innocuous. 



Raulin, in the course of the work referred to in the preceding section, had also 

 noticed that one part of silver nitrate in 1,600,000 of the culture medium was 

 sufficient to prevent germination of the spores of Aspergillus ; in fact, if the 

 medium is contained in a silver vessel, sufficient metal is dissolved to prevent 

 growth therein. 



Ringer and Phear did not attribute the toxic action of their distilled water to 

 " oligodynamic action," but Locke, in the paper quoted above, showed clearly that 

 the explanation lay in this fact, since distilled water condensed in glass had no 

 injurious action. 



It has been found that certain bright metals pass readily into the colloidal 

 state when placed in contact with pure distilled water (see Traube-Mengarini 

 and Scala, 1912). Thus lead, zinc, iron, tin, aluminium, copper, and nickel form, 

 in this way, colloidal solutions in which the dispersed phase is, at first, in the 

 metallic state, but subsequently becomes hydroxide. 



