4 SACBKOOD, A DISEASE OP BEES. 



of this disease changes much less than it does in foul brood. The 

 body wall is not easily broken, as a rule. On this account often the 

 entire larva can be removed from the cell intact. The content of this 

 saclike larva is more or less watery. The head end is usually turned 

 markedly upward. The dried larva or scale is easily removed from 

 the lower side wall. There is practically no odor to the brood 

 combs. 



THE INFECTIOUS NATUKE AND CAUSE OF SACBHOOD. 



In the study of samples of this disease received directly from bee 

 keepers no microorganisms have been found, either culturally or 

 microscopically, to which the cause of the disease can be attributed. 

 This fact, together with the fact that the disease often disappears 

 without any great loss to the colony, would tend to indicate that the 

 disease is not infectious. The experimental evidence which I have 

 obtained proves, however, that the disease is infectious. 



EXPERIMENTAL WORK WITH SACBEOOD. 



Evidence has been obtained by me that sacbrood can be trans- 

 mitted from diseased to healthy brood. Three healthy colonies were 

 inoculated each with diseased material from a different locality, and 

 in each of these three experimental colonies the disease was pro- 

 duced. These results indicated at once that sacbrood is an infec- 

 tious disease. The microscopical and cultural study of the infected 

 and dead brood in these experimental colonies, as in the case of the 

 diseased brood in samples direct from the apiary, failed to show 

 any organism to which the cause of the disease could be attributed. 



This led naturally to a study of the condition to determine whether 

 or not the virus of the disease was so small that it had not been seen. 

 To obtain evidence on this point material containing the virus was 

 filtered, using an earthenware filter. The three colonies in which 

 the disease had been produced experimentally furnished the disease 

 material for the experiments. Larvae, sick and dead, of sacbrood 

 were picked from the combs, crushed, and diluted with sterile water. 

 This suspension was filtered by the use of the Berkefeld filter. From 

 each of the three diseased colonies a separate filtrate was obtained, 

 which was fed in sirup to healthy colonies. Six colonies were thus 

 fed — two with each of the three separate filtrates. As a result of 

 these inoculations sacbrood with typical symptoms of the disease was 

 produced in all of the six colonies thus fed. 



One more experiment will be mentioned at this time. In this the 

 diseased brood used was taken from one of the colonies in which 

 the disease had been produced by feeding filtrate. Disease material 

 from this colony was filtered as before and fed to two healthy colonies. 



