RELATION OF ETIOLOGY OF BEE DISEASES TO TREATMENT. 37 
caused b} T bacteria. Above all, you should understand that the death 
of the brood is due to one species of bacteria growing in the larva?. 
Protozoa. — In contrast to bacteria, the protozoa belong to the ani- 
mal kingdom. They are very small unicellular animals. Many 
species are harmless, as are many species of bacteria, while some 
species have the power to produce disease. They produce disease 
and death in a manner very similar to bacteria; that is, by growing 
in the body of a living animal. As far as we know, none of the bee 
diseases is due to protozoa. One investigator described what he 
thought was a protozoon and named it Spirochceta apis. It was 
shown that he made an error in his observations. Therefore there is 
no Spirochceta apis and no protozoon, as far as we know, which is 
pathogenic to bees. 
Fungi, — The term " fungi " is a rather broad one, but in the dis- 
eases of animals we usually refer, in speaking of fungi, to those 
forms of plant life which are higher than bacteria. They are usually 
made up of branching mycelial threads, and have a variety of meth- 
ods for producing spores. One writer described one species, Aspergil- 
lus pollini, which he was supposed to have proved to be the cause of 
pickled brood, but he had not done so. 
To the above groups belong the known exciting causes. There are 
also unknown exciting causes. When the unknown causes become 
known they may be found to belong to the groups mentioned above. 
There is a very important classification of diseases into those which 
are infectious and those which are noninfectious. From what has 
been said, this classification becomes clear to us. An infectious bee 
disease is one which may be transmitted from one colony to another 
through the natural processes in the apiary. American foul brood 
and European foul brood are examples of this class of disease. What 
is transmitted in an infectious disease % It is the exciting cause of that 
disease. In American foul brood it is one species of bacteria, Bacillus 
larvce. In European foul brood we do not know what is transmitted. 
Since we do not know the exciting cause it must be classed under the 
unknown exciting causes. When the cause is determined it will prob- 
ably be found to belong to one of the three groups of micro-organisms 
mentioned under the known causes. A noninfectious disease is one 
which is not transmitted from one colony to another. The so-called 
" pickled brood " and paralysis, as far as we know, illustrate this class 
of diseases. 
This brief discussion of the etiology of disease is given in order 
that you may get a clearer idea of the nature of disease and what is 
meant by etiology. We shall now consider the treatment of disease 
and illustrate with bee diseases. 
