78 MICROBES AND TOXINS 



Sulphur is indispensable in the culture fluid of the sulphurous 

 o.r sulpho-bacteria (Beggiatoa, Lamprocystis, and other species 

 described by Winogradsky) ; these can do almost entirely 

 without organic food material and grow well in water which 

 contains only 4*8 milligrams of this per litre, but which contains 

 two milligrams of sulphuretted hydrogen. This they decompose, 

 fixing the sulphur and accumulating it in the cell in the same 

 way as yeasts with glycogen. Certain Beggiatoa contain 

 80-95 P er I0 f tnen " weight of sulphur. When put for two or 

 three days in non-sulphurous water they oxidize their sulphur 

 turning it into sulphates. If the dearth of sulphur continues 

 they die. 



The ferro-bacteria (e.g.^ Crenothrix polyspora^ Cladothrix 

 dichotoma, Leptothrix ochraced) oxidize the carbonate of 

 iron protoxide, FeH 2 (CO 3 ) 2 , and accumulate the hydrate of 

 ron oxide. Instead of iron oxide a deposit of oxide of 

 manganese has been observed in certain cases. 



The Importance of the Chemical Constitution 01 

 the Medium. Pasteur observed the relations between the 

 chemical structure of the food material and the physiological 

 action on it of the microbe. A Penicillium uses up dextro- 

 tartaric acid, leaving intact the laevo form until the former is 

 completely exhausted. Penicillium glaucum and certain 

 yeasts can decompose optically-inactive sugars, burning up the 

 dextrorotatory form while sparing the laevo. 



Following in the track of Emil Fischer, there have been 

 observed relations between the molecular constitution of a 

 sugar and its value as food or fermentable material to a yeast 

 or in general to any definite ferment. Among the numerous 

 sugars with the general formula C^H^On (n being a whole 

 number i, 2, 3, 4, etc.), the ordinary yeasts only ferment those 

 with the carbon atoms numbering 3 or a multiple of 3. Sugars 

 which are isomeric, but whose molecule does not possess the 

 same stereochemical configuration, do not behave exactly the 

 same towards a given yeast. In a mixture of glucose and 

 levulose one or other is the first to be decomposed, this varying 

 with the strain of yeast. 



