10 BIOCHEMISTRY OF FUNGI 



kinshaw (1937), Lockwood and Aioyer (1938), and Tatum (1944) 

 will be found very serviceable. 



In these biochemical researches it is of more than passing in- 

 terest to note that members of the cosmopolitan genera Aspergillus 

 and Penicillium have been very commonly employed. In fact, 

 Aspergillus niger is the biological agent in so many tests that it is 

 easy to understand why this species may appropriately be desig- 

 nated the "fungus guinea pig." This epithet may be applied 

 equally appropriately to Venicillium glaucum. The reason for the 

 use of these species and of closely related ones lies in their ability 

 to produce a wide variety of enzymes, making it possible for them 

 to utilize many kinds of substrata as foods, as is indicated in 

 Chapter 1. In the discussion that follows, emphasis will be placed 

 on the metabolic products formed by fungi, only incidental at- 

 tention being given to the influence of nutritional factors. (The 

 nutrition of fungi is considered separately in Chapter 1.) Inade- 

 quate emphasis must of necessity be placed upon the mechanisms 

 by which these metabolic products come into being, mainly be- 

 cause they are in many instances quite unknown or at least not yet 

 fully understood. 



ORGANIC ACIDS AND OTHER PRODUCTS HAVING 

 SIX OR FEWER CARBON ATOMS 



The foundations for our understanding of the genesis of organic 

 acids by fungi were established between 1896 and 1897 by the 

 classical studies of Wehmer. These studies involved the common 

 carboxvlic acids, but later observers have devoted themselves to 

 the production of acids belonging to other groups as well. Cer- 

 tain essentials regarding the mechanisms in these fermentations 

 have been elucidated by such workers as Bernhauer, Chrzaszcz, 

 Butkewitsch, Neuberg, Cohen, Raistrick, and Birkinshaw and 

 their associates and pupils. 



Oxalic acid. Wehmer (1891 ) observed that crystals of calcium 

 oxalate are present in the mycelium of Aspergillus niger and in the 

 culture medium in which this organism grows. He was first to 

 recognize that this acid is a by-product in the fermentation of a 

 variety of substrates and that with the addition of calcium carbo- 

 nate to the substrate very large yields may be obtained. Subse- 

 quently others have confirmed these findings with A. niger and 



