172 MICRO-ORGANISMS AND FERMENTATION. 



different phenomena of decomposition and splitting up due to 

 the vital activity of the organism. The most important of 

 the vital functions in this respect is that of respiration. The 

 two processes are intimately related to each other. During 

 respiration a large number of different nutrient substances 

 are transformed, and, in common with all other forms of life, 

 the final products are carbon dioxide and water. Amongst 

 the products formed under conditions of incomplete oxidation, 

 mention may be made of oxalic acid, which is of remarkably 

 wide occurrence in fungi. In addition to the usual respiration 

 of oxygen, a further form of oxidation in the absence of oxygen 

 may take place, to \vhich the term intramolecular respiration 

 or respiration by dissociation has been given. 



The following facts may be of interest in regard to the 

 individual substances that play a part in the nutrition of 

 fungi : Potassium appears to be essential to the growth of 

 moulds, particularly to the formation of their reproductive 

 organs. Within certain limits this element forms a useful 

 food for yeast, and the fact must not be overlooked that it 

 also plays a part in the nutrition of bacteria. Magnesium, 

 amongst the alkaline earths, is necessary for the generality 

 of moulds, as well as for yeasts and many bacteria. The 

 formation of colouring matter in many bacteria has been 

 shown to depend on the presence of magnesium in the nutrient 

 fluid. It may further be assumed that many fungi require 

 Calcium in order to attain perfect development. Iron appears 

 to be required by moulds either as a food or as a stimulant, 

 and, especially in the form of the sulphate, it exerts a favourable 

 influence on the propagation of yeasts. We can assume that 

 Sulphur is an essential element, since all albuminous substances 

 contain sulphur ; it is usually added to the nutrient solutions 

 in the form of a sulphate. Many fungi, however, seem to 

 be capable of developing in nutrient solutions to which no 

 addition of sulphur has been made. Sulphur plays a very 

 important part in the metabolism of the sulphur bacteria. 

 Phosphorus is assimilated by fungi in a variety of compounds, 

 and is, without doubt, a necessary constituent of their food. 

 The fluorescence exhibited by many bacteria depends upon 

 its presence. Nitrogen is, as is well known, of the greatest 



