564 ANNUAL REPORT OP THE Off. Doc. 



ferment is capable of producing very great chaoges. (b) They are 

 all dependent upon temperature as a condition of activity. They 

 cease to act at low and also at high temperatures. Most of them 

 find the temperature best suited to their greatest activity between 

 80 and 100 degrees F. (c.) Ferments are destroyed by heat, 

 the temperature of boiling water in most cases completely destroying 

 their power to act. Their activity is checked by low temperatures, 

 but, when again warmed, they reuev/ their activity, (d.) The pro- 

 ducts which ferments form, when accumulating m certain amounts, 

 usually stop further action, (e.) All ferments are closely connected 

 with life processes. 



I). Two General Glasses of Ferments. 



The different bodies that are capable of causing fermentations 

 may be divided into two general classes (1) organized ferments, and 

 (2) unorganized ferments. 



(1.) Organized Ferments are living organisms capable of produc- 

 ing fermentations. Those of greatest interest found in milk and its 

 products are called bacteria. Bacteria are the smallest conceivable 

 forms of plant life. Each individual consists of a single cell, aver- 

 aging in diameter one-thirty thousandth of an inch. They appear 

 in three general varieties of form : Ball (coccus), short rod (bacillus), 

 and cork-screw (spirillum). They multiply i^i number or reproduce 

 by simjjle division; that is, when a cell grows in size, it increases 

 more in one direction, so as to lengthen out slightly, and a partition 

 forms across the cell, thus producing two new cells in place of the 

 old one; and then each of these subdivides again and so on continu- 

 ously. Some kinds of bacteria form spores in the cells; these are to 

 bacteria what seeds are to higher plants. Spores are not so easily 

 killed by heat as are bacteria. Some bacteria have power of motion. 

 Under favorable conditions, their rapidity of growth is remarkable. 

 In some cases, one cell divides into two cells in twentv minutes; 

 if this raie were kept up for twenty-four hours, the one cell would 

 multiply into several millions. Bacteria require as food for satis- 

 factory growth compounds containing nitrogen, carbon, hydrogen, 

 and, in addition, small amounts of inorganic or mineral matter. 

 Che sugar, casein and albumiH io li^ilk and its products furnish a 

 supply of food very readily utilized by bacteria. As already stated, 

 bacteria are affected by temperature. The bacteria commonly pres- 

 ent in milk grow^ between the limits of 40 and 110 degrees F., the 

 most favorable temperatures being between 80 and 95 degrees F. 

 Many bacteria are killed between 130 and 140 degrees F.. when ex- 

 posed to this degree of heat for ten minutes, and most are destroyed 

 at 185 degrees F. Many spores are killed at temperatures con- 



