16 



BULLETIN 810, U. S. DEPAETMENT OF AGEICTJLTUKE. 



the food of the larvae by means of a capillary pipette made from 

 glass tubing of small bore. Care must be exercised in thus feeding 

 the larvae. Too much of the suspension will often float the larva. 

 There is danger also that it will be changed in position mechanically 

 by means of the feeding pipette. In either event the chances are 

 that such lars'ae will be removed subsequently by the bees. Consider- 

 able larval food already in the cell is advantageous. This method 

 has proved to be especially useful in much of the experimental work 

 recorded in the present paper. It has the advantage of being both 

 economical as to the number of colonies needed, and definite. Dur- 

 ing the third day following the 

 hour of inoculation symptoms 

 of European f oulbrood will be 

 observed if infection is pro- 

 duced. By the fourth day fre- 

 quently all of the infected lar- 

 vae will have been removed by 

 the bees. Symptoms of Euro- 

 pean f oulbrood infection mani- 

 fested by larvae sick rather than 

 dead have proved to be espe- 

 cially useful for experimental 

 purposes in these studies. 



During most of the time that 

 experimental studies are being 

 made it is necessary to have 

 fresh diseased material at 

 hand. A supply can be main- 

 tained by using one or more 

 colonies for this purpose. Re- 

 peated inoculations of the col- 

 ony usually must be made at intervals of a few days or after longer 

 periods, depending on its condition and the need for the virus. The 

 indirect method is especially indicated in inoculating these colonies. 



Frequently colonies which have been employed in European foul- 

 brood experiments can be used again for further experiments on the 

 disease. This must be done with some care, however. The condition 

 of the brood always should be noted before an inoculation is made. 

 European foulbrood colonies serve very well the purpose of experi- 

 mental colonies for the other brood diseases and for Nosema-disease. 

 In fact, not infrequently during these studies experiments on two or 

 more of the diseases were in progress in a colony at the same time. 



The apiary (PI. VI) used in the experimental work with European 

 foulbrood was the same as the one employed in the study of sac- 

 brood ( ir ) , Nosema-disease ( 18 ) , and American foulbrood ( 19 ) . The 

 hive (fig. 6) and the experimental colonies, where they were not the 



Pig. 6. — Experimental hive, having 4 Hoffman 

 frames, a division board, Petri dishes as feed- 

 ers, the entrance nearly closed with wire 

 cloth, and the opening on the side of the 

 hive body occupied by the frames. (Author's 

 illustration.) 



