50 AGRICULTURAL BACTERIOLOGY 



material may be physiologically dry for one form of life and 

 not for another. The growth of molds on bread, cheese, 

 dried meats, paper, and clothing is evidence of their ability 

 to grow in the presence of a small percentage of water. 



If a cell is transferred from a concentrated solution to 

 one that is less concentrated, the water will be drawn into 

 the cell and may cause the rupture of the cell wall. The 

 term plasmotypsis is applied to this process. 



Many of the bacteria can not withstand desiccation, the 

 cells being almost immediately destroyed. Still others can 

 remain alive in a dried condition for long periods of time. 

 Their resistance to desiccation becomes of importance in 

 disease transmission. The bacterial spores are extremely 

 resistant to drying. Yeasts are, in general, less easily in- 

 jured by desiccation than are the bacteria. The mold 

 spores are very resistant to drying. 



Temperature. As is well known, decomposition goes on 

 more rapidly as the temperature is increased, up to a cer- 

 tain limit. This, of course, implies that the growth of the 

 microorganisms is accelerated as the temperature rises. 

 The temperature at which any organism thrives most rap- 

 idly is known as the optimum temperature for that organ- 

 ism. As the temperature changes from the optimum, the 

 rate of growth decreases. As a rule, a few degrees above 

 the optimum temperature, growth is no longer possible. 

 The maximum temperature has been reached. As the tem- 

 perature falls below the optimum, the rate o.f growth is 

 reduced until a point is reached at which it ceases. This 

 is known as the minimum temperature, and is, as a rule, 

 far below the optimum temperature. 



The temperature zone in which growth of bacteria is pos- 

 sible varies widely with different organisms. In the case 

 of some, it is but a few degrees in extent ; with others, it 

 may be very wide, ranging from the freezing-point to that 



