11 



THE ESSENTIALS. 



If a quantity of green material is cut and made up into 

 a small heap, it is common knowledge that under ordinary 

 conditions as to temperature it will rot,, and instead of 

 the feeding value of the resulting material being increased, 

 it is on the contrary strongly repulsive to stock. 



It is known that rotting or putrefaction is a process by 

 which organic matter, and particularly the nitrogenous com- 

 pounds in the cut parts of the plant, are decomposed into 

 simpler substances such as nitrogen, hydrogen, carbon 

 dioxide, ammonia, sulphuretted hydrogen, and other similar 

 gases, and it is the evil-smelling properties of some of these 

 gases which give to a rotting mass its unpleasant odour. 



The cause of this decomposition, which is termed putre- 

 faction, is the action of various species of minute organisms 

 or bacteria, and it is the nature of the bacteria engaged 

 on which depends the amount and kind of the rotting. It 

 is not then simply exposure to air which causes rotting. 

 Both fermentation and putrefaction can only take place 

 when certain living organisms are present, and the condi- 

 tions are suitable to their action. At a temperature below 

 freezing point the activity of the bacteria, which under 

 more favourable conditions would cause meat to go bad, is 

 suspended. On this fact the successful traffic in frozen 

 moat is carried on. 



So also do the products of fermentation vary in amount 

 and kind according to the conditions of temperature 

 present. 



We all know that milk is more apt to develop a sour taste 

 in warm weather than in cold. The reason for this is that 

 the activity of the bacteria which produce the lactic acid is 

 greatest at a temperature of from 30 to 35 degrees centi- 

 grade. We also know that if, immediately after milking, 

 we cool down the milk and keep it at a low temperature, the 

 injurious results of bacterial activity will be delayed. 



If subjected on the other hand for some time to a tem- 

 perature of, say, GO degrees centigrade, the lactic acid pro- 

 ducing bacteria arc killed. If the milk was then allowed 

 to cool and kept free from further infection, it would not 

 undergo a lactic fermentation, although in time it might 

 spoil by the action of other bacteria which had not been 

 killed by a temperature of 60 degrees centigrade. 



Thus we see that different species of bacteria are suited 

 to different temperatures, so that if matter rises in tempera- 

 ture over certain points, one set is rendered inactive, if 

 not killed, and another species, which before did not 



