182 MICRO-ORGANISMS AND FERMENTATION. 



The action of dilute acids and alkalies is also very varied. 

 Thus, minute quantities of free hydrochloric acid (a^Vo- of 

 normal acid) greatly increase the activity of invertase. 



The action of enzymes is to a great extent analogous to- 

 that of hot acids (hydrolysis). 



The formation of the enzyme by the fungus is dependent 

 to some extent on nutrition, as already stated in the chapter 

 on bacteria. Aspergillus glaucus, for instance, as Duclaux has 

 shown, when cultivated on a solution of calcium lactate and 

 nutrient salts, secretes diastase, but no invertase. On the 

 other hand, on a solution of cane sugar and nutrient salts, 

 invertase is produced, but no diastase nor any other enzyme 

 that it is capable of producing. Only by cultivating the 

 fungus on milk is it capable of producing clotting enzymes 

 and casease. Similarly, it was discovered by .Went that a 

 species of Monilia, which possesses a number of enzymes, 

 could only form certain of them, such as trypsin and the 

 clotting enzyme, when substances capable of being split up 

 were present. Fermi proved that several kinds of bacteria, 

 w.hen cultivated on media free from albumen, formed no- 

 albumen-splitting enzymes, and that Bacillus subtilis only 

 produced diastase when fed with some form of peptone. 



In fungi, moreover, a number of poisonous substances 

 occur ptomaines, toxins, etc. These are not to be regarded 

 as produced exclusively by the higher fungi (toadstools, etc.), 

 but occur also in the lower forms, such as rusts and smuts, 

 which have brought about cases of poisoning. Reference may 

 also be made to the extremely poisonous nature of Asper- 

 gillus fumigatus and A. flavescens. 



The carbohydrates which have been shown to occur in 

 fungi include glucose and laevulose ; mannite is very widely 

 distributed, and glycogen, to which we shall return in the 

 chapter on alcohol-producing yeasts, generally occurs as- 

 reserve substance. 



Fats and free fatty acids are found as reserve substances, 

 and as secretions in many fungi. Penicillium and Aspergillus, 

 for example, have been shown to contain from 4 to 5 per 

 cent, of these substances. Yeast stores up fat along with 

 glycogen, the former constituting from 2 to 5 per cent, of 



