474 CHEMICAL AGENTS 



gram of spores per hour, almost 300 times the rate of the same process 

 in Rhizopus nigricans. In these experiments there was no external 

 hydrogen donor, so that cell constituents must have been oxidized; it 

 is found, as would be expected, that under such circumstances high 

 rates of hydrogen sulfide evolution are not maintained for long. An- 

 aerobically, the formation of hydrogen sulfide from sulfur is accompa- 

 nied by an equivalent release of carbon dioxide; aerobically, sulfur 

 increases oxygen uptake (246b). 



Mycelium of Fusarium lini is similarly capable of reducing elemen- 

 tary sulfur in the presence of isopropyl alcohol as hydrogen donor (369). 



Fungi of different species differ very markedly in their sensitivity to 

 sulfur under field or laboratory conditions; of the common test fungi 

 for example, Stemphylium sarcinaeforme is about 60 times as resistant 

 as Monilinia fructicola (Table 2). However, it has not yet been possi- 

 ble to correlate the enzymatic reduction of sulfur with its fungitoxicity 

 — fungi which are relatively tolerant of sulfur are numbered among 

 both those most active and those least active in reducing sulfur, whereas 

 the more sulfur-sensitive species tend to be intermediate in reducing 

 capacity (289). However, this type of study has only begun, and it is 

 not yet possible to exclude any hypothesis with finality. 



The production of large amounts of hydrogen sulfide from elemental 

 sulfur in the absence of external hydrogen donors suggests that some 

 relation may in the future be established between the derangement of 

 metabolism associated with this process and the toxicity of sulfur (289). 

 It is clear that sulfur is competing with normal hydrogen acceptors, and 

 two speculative hypotheses are suggested by this conclusion. The first 

 may be expressed, rather crudely, by the proposition that in the pres- 

 ence of very large amounts of a suitable hydrogen acceptor, sulfur, de- 

 hydrogenation reactions escape from the normal control imposed upon 

 them under anaerobic conditions. This normal control may be either 

 the limited supply of acceptors for "high-energy" phosphate or a poi- 

 soning of metabolism by the accumulation of such fermentation prod- 

 ucts as ethanol; the first of these is the more likely. The physiological 

 effect of such an escape from regulation would be the disappearance 

 of the cell's reserves. According to this hypothesis, sensitivity would be 

 a function of the amount of utilizable reserve materials available to the 

 spore and should be reduced by provision of an external hydrogen 

 donor. 



A related hypothesis to explain a deleterious effect of the reduction 

 process itself is that utilization of reserves per se is less important than 

 the fact that provision of sulfur results in a series of oxidations which 

 are not coupled to the energy storage and energy utilization mechanisms 



