ENZYMES AXD OTHER FERMENTS DIGESTION. 143 







mentations when the water is mixed with some sterilized milk, 

 as in one of the common tests carried out in the sanitary ex- 

 amination of water. Garden soils are also rich in some of 

 these butyric acid-producing organisms, and may be used in 

 starting a fermentation, as may be illustrated in this way : 



Ex. Mix 100 cc. of a 5 per cent glucose solution with four or five 

 grams of fibrin and heat to boiling. To the hot solution add a few grams 

 of garden loam and allow the liquid to cool rapidly. The bacterial spores 

 resist the heat while other forms succumb and are thus disposed of. Keep 

 the mixture at a temperature of about 37 to 40 C Fermentation begins 

 in about two days and is assisted by neutralizing with a little sodium 

 hydroxide from time to time. After several days the presence of butyric 

 acid may be shown by warming some of the liquid with sulphuric acid, 

 or with sulphuric acid and alcohol. In the latter case the odor of ethyl 

 butyrate formed is very characteristic. 



Butyric acid in pure condition is a strongly acid liquid pos- 

 sessing a rather disagreeable odor. It is frequently present 

 in the stomach, but its occurrence there is really abnormal. 

 If the gastric juice contains the proper amount of hydrochloric 

 acid a butyric acid fermentation is not possible. With dimin- 

 ished hydrochloric acid, however, bacterial fermentations can 

 take place. In the arts while lactic fermentation is desirable 

 frequently, and encouraged, the butyric fermentation is usually 

 considered very objectionable and is prevented if possible. 



Other Fermentations. It will not be necessary to explain 

 at length any other cases of bacterial fermentations, as these 

 two just given are sufficient for illustration. What is known 

 as the mucous fermentation sometimes takes place in sacchar- 

 ine liquids or in wines which have not been completely fer- 

 mented. A slimy mucilaginous product is formed here which 

 contains a kind of gum. Certain microorganisms have the 

 power of decomposing cellulose and the operation is called the 

 cellulose fermentation. The products of this reaction with 

 certain bacteria are mainly gaseous, hydrogen and marsh gas 

 predominating. Certain organisms are able to produce fatty 

 acids also. In the intestines of the herbivora changes of this 

 character take place, and the acids produced are doubtless of 

 value 'in aiding in some of the other digestive processes which 

 take place there. 



