16 BULLETIN 810, U. S. DEPARTMENT OF AGRICULTURE. 
the food of the larve by means of a capillary pipette made from 
glass tubing of small bore. Care must be exercised in thus feeding 
the larve. Too much of the suspension will often fioat 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 larve 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 foulbrood will be 
observed if infection is pro- 
duced. By the fourth day fre- 
quently all of the infected lar- 
ve will have been removed by 
the bees. Symptoms of Euro- 
pean foulbrood infection mani- 
fested by larve 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 
vi made it is necessary to have 
Fic. 6.—Experimental hive, having ¢ Hoffman frech diseased material at 
frames, a division board, Petri dishes as feed- 
ers, the enirance nearly closed with wire hand. A supply can be main- 
~cloth, and the opening on the side of the’ tained by using one or more 
ey Li) Loan fo eolenies forgine plea pai 
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 (Pl. VI) used in the experimental work with European 
foulbrood was the same as the one employed in the study of sac- 
brood (17), Nosema-disease (18), and American foulbrood (19). The 
hive (fig. 6) and the experimental colonies, where they were not the 
