I9I4] Arthur W. Dox 225 



it even had a depressing effect when added to media free from mag- 

 nesium. 



The f act that phosphorus cannot be replaced by arsenic ; sulphur 

 by selenium or tellurium; potassium by the other alkali metals; 

 magnesium by glucinum, calcium or the rare earths, indicates that 

 these Clements are essential as nutrients. 



With the zinc and iron in Raulin's medium the case is quite 



different. Their function is purely that of a catalyser or stimulant. 



Javillier and Sauton^*'' studied the effect of these two Clements on 



the nutrition of Aspergillus niger. In the presence of zinc (o.ooi 



per Cent. ) and the absence of iron, spores did not appear even af ter 



the fourth day. When zinc was absent and iron present (o.ooi 



per Cent.) black spores appeared in two days, although the growth 



was less luxuriant than in the control culture. With both zinc and 



iron absent, the thin mycelium produced spores as rapidly as in the 



presence of iron alone. Cultures on zinc and iron together showed 



a normal amount of growth with spores on the fourth day. Iron 



is therefore not indispensable for spore formation as had been pre- 



viously supposed. An interesting Observation was the failure of 



the medium to give the sulphocyanate reaction when both zinc and 



iron had been omitted. In the absence of zinc, the sucrase^^ of the 



mycelium was reduced 30 per cent. The enzyme failed to diffuse 



into the medium or into distilled water, as it does ordinarily. 



Javillier^ ^ belle ves that the zinc regulates the consumption of 



sucrose, rendering the growth of the plant more economical. 



This view is held also by Buromsky^^ who finds that zinc increases 



CO» 



the respiration coefficient, — r-r- — ■— , and diminishes the 



^ weight of lungus 



sucrose 



economic coefficient, — t-t~ — 7-7 . 



weight of lungus 



The non-specificity of zinc as a catalyser was established by 



Lepierre, who succeeded in replacing the zinc of Raulin's medium 



by a number of other metals. He found, for example, that cad- 



mium^*^ can replace zinc and, like the latter, accelerates the growth 



16 Javillier and Sauton: Compt. rcnd., 153, 1177-80 (1911)- 

 IT Javillier: Ibid., 154, 383-6 (1912). 



18 Javillier: Ibid., 155, 190-2 (1912). 



19 Buromsky : Loc. cit. 



20 Lepierre: Compt. rend., 156, 25S-61 (1913). 



