166 Agricultural Bacteriology. 



black leg and anthrax. The most important and most 

 common of the diseases affecting the domestic animals 

 are caused by bacteria that do not form spores. 



Disinfectants. Disinfecting agents may be divided 

 into two classes, physical and chemical. The effect of 

 the most important physical disinfectant, sunlight, has 

 been discussed in a previous chapter. Sunlight rapidly 

 destroys all vegetating bacteria and their spores as well, 

 if it falls directly upon them. If, however, they are cov- 

 ered with a layer of dirt or dust even though it be very 

 thin, the sunlight has little effect on them. Diffuse light, 

 such as is present where the direct rays of the sun do not 

 penetrate, is very weak in its action, requiring hours and 

 days to produce the same effect as a few moments of di- 

 rect sunlight. It is very certain that sunlight under the 

 conditions that obtain in barns and stables has but little 

 disinfecting action, because of the fact that the bacteria 

 are protected from its action by the dirt and dust. 



Another physical agent of which little use can be made 

 in the disinfection of stables is heat, either as dry heat or 

 in the form of steam or hot water. Any small object of 

 wood or iron can be easily disinfected by boiling. Thus, 

 in the case of contagibus diseases of human beings, this 

 process is frequently used. In the disinfection of stables 

 etc., one is limited to the use of chemicals. 



Chemical disinfectants. The chemicals used for dis- 

 infection may be divided into two classes, solid materials 

 used in suspension or in solution, and gaseous. The lat- 

 ter are by far the best when the conditions will permit of 

 tneir use for the gas penetrates to every part of the space 

 to be treated, even into cracks and crevices. This fact 

 makes their use impossible except in a space that can be 

 tightly closed, for the gas must be confined for several 



