46 BULLETIN 780, IT. S. DEPARTMENT OF AGRICULTURE. 
MODES OF TRANSMISSION OF NOSEMA-DISEASE. 
No problem in the study of Nosema-disease is more important than 
that of its transmission. The problem is at the same time one of 
the most difficult for complete solution. While further information 
is still much desired, yet it is possible from the studies which have 
been made to arrive at certain conclusions concerning the manner 
in which the disease is spread. The discussions which follow are 
based chiefly upon observations noted in the foregoing pages. 
It is naturally safe to conclude that the transmission of Nosema- 
disease depends directly upon the transmission of the parasite that 
causes it. If the course of Nosema apis in nature were followed 
completely, therefore, the problem relative to the spread of the disease 
would be solved. Such a task is difficult, as the possible sources 
for the parasite and the accompanying conditions are various. 
The fact, determined experimentally, that a suspension of Nosema 
apis in sirup when fed to bees will produce the disease shows quite 
conclusively that infection takes place through the ingestion of the 
parasite. At present there is no evidence that it takes place other- 
wise than by way of the alimentary tract. This leads to the im- 
portant tentative conclusion that the transmission of the disease is 
effected through either the food or the water supply of bees, or both. 
On reaching the stomach by ingestion the parasite begins its growth, 
invades the walls of the organ, multiplies enormously, and forms 
spores which are shed into the lumen and passed out of the alimentary 
tract with the excrement. The chances that any single parasite once 
outside the bee will be ingested and cause infection are very slight. 
The immense number that are produced, however, increases the 
chances very greatly. Again, the chances of infection are very much 
reduced by the many destructive agencies in nature encountered by 
the parasite. Among these are drying (p. 31), heat (p. 29), direct 
sunlight (p. 37), fermentation (p. 33), and putrefaction (p. 35). 
The excrement is voided normally during flight and most often 
soon after the bee leaves the hive. Should the droppings from in- 
fected bees fall into a body of water, such water would become 
thereby contaminated with the Nosema parasite and the use of it 
by bees would expose them to infection. Should the body of water 
be a rapidly flowing one, naturally the chances that other colonies 
of the apiary might become infected from such a source would be 
less than if it were a sluggish one. Should such contaminated water 
be exposed to the sun, the rays of the latter would have a tendency 
to destroy the parasites. The resistance of Nosema apis to the de- 
structive effects of the sun's rays (p. 38) are sufficiently great, 
however, that there would still remain a strong likelihood that infec- 
tion might take place from the water supply. While in the water 
