2QO 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 il 
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 ir 
handling bees. It is also doubtless carried from locality to locality 
by the custom of selling bees. The two diseases are widespreac 
over America, Europe, Africa, and Australia. It spreads rapidly 
sometimes infesting a whole district in the course of a single seasor 
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 b} 
microorganisms too small to be seen by our microscopes. That the) 
are caused by living agents of extremely minute size is shown by twc 
series of facts: i. Material may be obtained from animals suffering 
from the disease which will produce the disease in others, but its powei 
is destroyed by the same disinfectants as those used to kill bacteria 
2. The infectious agent will pass through porcelain filters, 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 pas< 
through them. There are other reasons for the conclusion, bui 
they cannot be given here. Although these organisms have nevei 
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 itsell 
chiefly in the mouth and feet of cattle, varies much in its severity 
Although not often causing death, it does result in great financia 
losses to dairymen. It is readily transferred to other animals 
most kinds being susceptible to it. It occurs rarely in man, bein^ 
