PRODUCTS OF THE LOWER FUNGI 283 



products, whilst liydi'ugeii is a very comiuoii product of 

 bacteria and methane is formed comparatively frequently. 



The function that these very varied compounds 

 perform is still in very large measure unknown. The 

 carbohydrates and fats probably serve as storage or 

 reserve materials as also may such acids as gluconic and 

 citric acids. Some products, such as the yellow pigment, 

 citrinin, may play the part of oxidation-reduction systems. 

 Other substances may exert a protective effect by 

 depressing or inhibiting the growth of other organisms. 

 For example, many moulds develop such acid conditions 

 (jjH 1 to 2) that bacterial growth is stopped. An inter- 

 esting case is the production by Pemcillium notatum and 

 P. chrysogenum of the antibiotic penicillin which has 

 marked specific bactericidal powers ; in very high dilution 

 it entirely suppresses the growth of the pyogenic cocci 

 and organisms of the diphtheria group, but it is easily 

 tolerated in higli concentration by other organisms such 

 as those of the coli -typhoid group, the influenza bacillus and 

 the enterococci. Many other antibiotic substances are 

 now loiown (see Chapter XI). 



In considering the metabolic products of the lower 

 fungi it must be remembered that they are essentially 

 aerobic organisms. If an adequate supply of air is 

 available they usually completely oxidise, to carbon 

 dioxide and water, not only the carbohydrate originally 

 present in the medium but also the metabolic products 

 which they themselves have formed. Consequently the 

 incubation periods allowed for formation of the products 

 must not be too long or low yields result ; the fermenta- 

 tions are usually stopped just before all the initial nutrient 

 substance has been used up. 



Acid Production by Fungi 



Acids of a wide variety of structures are synthesised 

 by the lower fungi from glucose as the sole source of 

 carbon. A list of them is provided in Table 19. 



