ACID DESTRUCTION AND PRODUCTION. 417 



306. The Destruction and Production of Acid in 

 Nutrient Liquids by Mycoderma. 



This matter has been thoroughly investigated by MEISSNER 

 (XI.), who obtained the following important results: The previous 

 researches of other workers, such as KOCH (V.), WORTMANN (XV.), 

 and WILL (XIII.), on the physiological behaviour of Mycoderma 

 revealed the fact that these fungi do not invariably lessen the 

 acidity of grape juice, wine, beer, &c. ; but that some races in par- 

 ticular produce acid, often in considerable quantity. MEISSNER 

 (XI.) explains this phenomenon by stating that Mycoderma are 

 able to form acids, as well as to destroy them, both processes 

 going on concurrently. The preponderance of the formative or 

 destructive action depends both on the powers of the various 

 races and on external conditions, such as the amount of oxygen 

 admitted to the cultures, the quantity of nutrient solution present, 

 &c. If the acid-forming capacity prevails, the total effect is an 

 increased acidity of the medium, and vice versa ; whilst if the 

 two powers be equal, the quantity of acid remains unaltered. 



In order to obtain a satisfactory insight into the nature 

 of the process whereby a reduction of acidity is effected 

 in liquids inhabited by Mycoderma, MEISSNER (VI.) closely 

 examined the behaviour of these fungi when grown on artificial 

 nutrient media (containing the necessary mineral ingredients) 

 with different organic acids as the sole source of organic matter. 

 The effect on malic acid was insignificant in certain races, but 

 very strong in others. One species, isolated from Colmar wine, 

 consumed within thirty-five days 5.72 grms. per litre (i.e., 73 per 

 cent.) of the malic acid originally present in the artificial medium, 

 the growth of the organism increasing in luxuriance with the 

 extent of decomposition attained. Tartaric acid proves generally 

 ill adapted for the building up of Mycoderma cells, and is therefore 

 consumed to only a small extent by the fungus. The same results 

 were obtained by SEIF*:RT (II.). The case is different with lactic 

 acid, MEISSNER (VI.) finding that six out of nine stocks examined 

 consumed this acid extensively, the other three to only a small 

 degree corresponding with their scanty growth. One race from 

 Silesian perry reduced the lactic acid content of the solution 

 (originally 0.7633 per cent.) to 0.0673 P er cent - Citric acid and 

 succinic acid were also attacked, sometimes extensively. In the 

 former case, the acid was almost entirely consumed in one-third 

 of the tests performed, whilst with the other acid, a similar result 

 was obtained in one-fourth of the tests : see MEISSNER (VII.). 

 In one-half of the same worker's experiments (VII.), acetic acid 

 was vigorously attacked, but only slightly in three instances, 

 whilst in three other cases the sowings failed to develop at all. 

 H. VAN LAER (VIII.) in examining one race of Mycoderma found 



