80 Dairy Bacteriology. 



cerned in this change are unable to develop in the presence 

 of lactic acid bacteria, so the addition of a clean sour milk 

 as a starter restores the normal conditions by giving the 

 ordinary milk bacteria the ascendency. 



Chemical disinfection. In exceptional instances it may 

 be necessary to employ chemical disinfectants to restore 

 the normal conditions. Of course with such diseases as 

 tuberculosis, very stringent measures are required, as they 

 are such a direct menace to human life, but with these 

 abnormal or taint-producing fermentations, care and clean- 

 liness, well directed, will usually overcome the trouble. 



If it becomes necessary to employ chemical substances 

 as disinfecting agents, their use should always be preceded 

 by a thorough cleansing with hot water so that the germi- 

 cide may come in direct contact with the surface to be 

 disinfected. 



It must be borne in mind that many chemicals act as 

 deodorants, i. e., destroy the offensive odor, without destroy- 

 ing the cause of the trouble. 



Sulfur is often recommended as a disinfecting agent, but 

 its use should be carefully controlled, otherwise the vapors 

 have but little germicidal power. The common practice of 

 burning a small quantity in a room or any closed space for 

 a few moments has little or no effect upon germ life. The 

 effect of sulfur vapor (S0 2 ) alone upon germ life is relatively 

 slight, but if this gas is produced in the presence of mois- 

 ture, sulfurous acid (H 2 S0 3 ) is formed, which is much 

 more efficient. To use this agent effectively, it must be 

 burned in large quantities in a moist atmosphere (three Ibs. 

 to every 1,000 cubic feet of space), for at least twelve hours. 

 After this operation, the space should be thoroughly aired. 



Formalin, a watery solution of a gas known as form- 

 aldehyde, is a new disinfectant that recent experience has 



