454 MICROBIOLOGY OF SPECIAL INDUSTRIES 



the cell contents of the organisms. For every organism there is a 

 maximum concentration reached sooner or later, beyond which growth ' 

 is impossible. 



Dried foods may be divided into three groups, using the relative 

 abundance of cdrbehydratesjfats, and proteins as a basis for classification. 



Carbohydrate foods are usually preserved by drying. Many, such 

 as grains and nuts and the flours and meals prepared from them, do 

 not require artificial i heating. . They are, however, somewhat hygro- 

 scopic and in damp climates enough moisture is taken up to allow ithe 

 growth of injurious molds and bacteria. Moldy corn has long been 

 regarded as the probable cause of the disease, called pellagra, in man. 

 'Still other carbohydrate food stuffs require more or less care in the dry- 

 ing or curing, such as hay and fodder in general. This is usually dried 

 by simple exposure to the air and sun until most of the water has been 

 evaporated. Fodder that has become moldy through the presence of 

 too much moisture is a prolific cause of trouble in horses and less fre- 

 quently in cattle. The many deaths due to the so-called cerebrospinal 

 meningitis are suspected many times to be due to the consumptictti of 

 moldy hay. In localities where the air is too moist or it rains so fre- 

 quently as to make it difficult to dry hay, curing is effected by a process 

 of, self fermentation. The hay is piled in a mass while still green and 

 undergoes a. process of heating. The temperature rises usually to about 

 70°. The causes of this rise are somewhat uncertain, but it is prob- 

 ably due to the combined action of enzymes and microorganisms. 

 Just how much of this keeping quality is due to the heating, how much 

 to the loss of water, and how much to the accumulation of products of 

 fermentation is uncertain. In other cases, the heated hay is spread out 

 and quickly dries , sufficiently so that it may be stored. A certain 

 small percentage of the nutriment of the hay. is necessarily lost in 

 the development of the heat energy. 



Fruits are quite generally preserved by drying. In many instances, 

 as in peaches, apples, and berries, it is probable that enough moisture 

 is usually removed to prevent organisms from growing, but in many 

 other cases, as in the preparation of currants and raisins, the concen- 

 tration of the sugar and other solutes is the controlling factor. Fre- 

 quently as much as 30 per cent of the dried fruits is water. Fruit dry- 

 ing is often accomplished, by the heat of the sun's rays, in other cases 

 artificial heat or even hydraulic presses are used. 



