290 OTHER GERM DISEASES. 



the European by B. alvei and the American by B. larva. In this 

 country the latter is the more common, though both are found. 

 Both diseases are readily carried from hive to hive. Sometimes this 

 is done by robber bees that steal honey from hives, and sometimes it 

 is carried by the bee-keeper who handles a diseased colony and then 

 a clean colony, or who places in a clean hive honey or combs from an 

 infested hive. Its very infectious nature should be thoroughly ap- 

 preciated by the bee-keeper and great care should be taken in 

 handling bees. It is also doubtless carried from locality to locality 

 by the custom of selling bees. The two diseases are widespread 

 over America, Europe, Africa, and Australia. It spreads rapidly, 

 sometimes infesting a whole district in the course of a single season 

 so as nearly to ruin the industry of the bee-keeper. 



DISEASE CAUSED BY UNKNOWN PARASITES. 



The causes of several well-known diseases have not yet been dis- 

 covered; nevertheless it must be recognized that they are caused by 

 microorganisms too small to be seen by our microscopes. That they 

 are caused by living agents of extremely minute size is shown by two 

 series of facts: i. Material may be obtained from animals suffering 

 from the disease which will produce the disease in others, but its power 

 is destroyed by the same disinfectants as those used to kill bacteria. 

 2. The infectious agent will pass through porcelain niters, whose 

 pores are too small to permit even the smallest bacteria to pass, 

 while it will not pass through some of the very fine porcelain filters 

 with pores still smaller, but large enough to allow liquid to pass 

 through them. There are other reasons for the conclusion, but 

 they cannot be given here. Although these organisms have never 

 been seen, quite a little is known of their general nature. The 

 animal diseases produced by invisible organisms are the following. 



Foot-and-mouth Disease. This disease, manifesting itself 

 chiefly in the mouth and feet of cattle, varies much in its severity. 

 Although not often causing death, it does result in great financial 

 losses to dairymen. It is readily transferred to other animals, 

 most kinds being susceptible to it. It occurs rarely in man, being 



