270 PHYSIOLOGY OF THE FUNGI 



(Psalliota) campestris. The method of cultivating this species on com- 

 posted horse manure was developed near Paris before 1700. For informa- 

 tion on mushroom growing the reader is referred to Duggar (1915). 



While attempts to replace composted horse manure by other substrates 

 have been made, none appears to be entirely satisfactory. Humfield 

 (1948) has suggested that Psalliota campestris be grown in large fermentors 

 and the mycelium rather than the fruit bodies be used for food. Aspara- 

 gus butt juice, a waste agricultural product, is a suitable medium. The 

 chemical composition of mycelium and that of the fruit bodies is similar 

 and the flavor comparable. This approach perhaps offers a way to culti- 

 vate other desirable species, including the morels and the truffles. Nord 

 (1948) has suggested that the mycelium of Fusarium lini be used for food. 



The use of yeasts to convert low-grade carbohydrates, such as wood 

 sugar and molasses, into food has interesting possibilities. It is necessary 

 to fortify these carbohydrates with other nutrients for the cultivation of 

 yeast. Phosphates, a source of potassium, and nitrogen, in the form of 

 urea, ammonia, or ammonium salts, are added. The function of yeast is 

 to convert inorganic nitrogen into protein. Animals are unable to 

 assimilate ammonia or urea directly but require nitrogen in the form of 

 protein or amino acids. Inorganic nitrogen may be converted into 

 proteins by green plants or by certain microorganisms. The use of urea, 

 a derivative of ammonia, as cattle fodder is an example of the synthesis 

 of protein by the microflora of the rumen. 



The possibility of using wood waste for yeast propagation was investi- 

 gated in Germany during the First World War. In 1944 it is reported 

 that 9,000 tons of food yeast were produced in Germany. Fermentable 

 carbohydrates are obtained from wood as a by-product of sulfite paper 

 manufacture, or by direct hydrolysis. Before sulfite liquor or wood 

 hydrolysate is used for yeast culture, it is treated with calcium carbonate 

 to adjust the pH and precipitate impurities. After the addition of 

 nutrients the solution is heavily inoculated with the desired strain of 

 yeast. Aeration is necessary for high yields of yeast. The weight of 

 yeast produced amounts to about half the weight of sugar utilized. Such 

 yeast is approximately 50 per cent protein (Harris et al., 1948). The 

 economics of fodder-yeast production from sulfite liquor have been studied 

 by Schleef (1948). The use of by-product molasses for the production 

 of food and fodder yeasts should offer fewer technical difficulties than the 



use of wood sugar. 



FAT PRODUCTION 



Serious efforts to utilize fungi for the synthesis of fats were made in 

 Germany during the First World War and continued thereafter. The 

 technical problems encountered proved difficult, but some success was 

 achieved by 1942 (Hesse, 1949). The controHing factor in fat production 



