14 Department Circular 28^^, U. S. Dept. of Agriculture 



PERMEABILITY OF CAPPINGS 



A. simple experiment was undertaken in an effort to learn whether 

 the permeability of the cappings is variable. Such a variation might 

 account for the fact that sealed cells are not always sterilized, and 

 for the variation in the number of cultures of Bacillus larvae from 

 sealed cells in different combs. 



If cappings are carefully removed from a piece of comb and 

 examined under the microscope, it is seen that their structure is 

 apparently very variable. The cappings are composed of criss- 

 crossing cocoon fibers, pollen grains, and granules of wax, and conse- 

 quently vary in structure. Cappings from brood cells of different 

 ages are found to vary greatly in thickness. Freshly sealed cappings 

 are much thicker and more opaque than cappings from the cells of 

 more nearly matured pupae, the latter often being gnawed by adult 

 worker bees. 



A simple piece of apparatus was devised to test the variability in 

 porosity of cappings. A piece of glass tubing slightly smaller in 

 outside diameter than the inside diameter of worker cells was drawn 

 to a fine capillary tube and broken off, making a capillary opening 

 on the end of a 6-inch tube. Numerous pappings were then removed 

 from various samples of comb, both diseased and healthy, with a 

 sharp scalpel, and cut so as to leave on the capping a rim of cell 

 wall about one-sixteenth to one-eighth-inch wide, care being taken 

 not to rupture the capping. These cappings were then sealed on the 

 larger end of the glass tube with liquefied beeswax. The end of 

 the tube covered by the capping was then submerged 3 centimeters 

 below the surface of the chosen disinfectant, so as to have a uniform 

 upward pressure on all the cappings successively tested. The rise 

 of the liquid in the tube was measured at the end of a five-minute 

 period unless the liquid was able to pass rapidly through the cap- 

 ping and to rise to the level of the outer liquid in less than that 

 time. The capillary opening in the upper end of the tube somewhat 

 retarded the exit of air and, unless the capping was cracked, or 

 slightly perforated, the contained liquid would not reach the level 

 of the outside liquid in five minutes. When the rise was more rapid 

 the apparent reason was recorded. A considerable number of cap- 

 pings were tested with fresh and used alcohol-formalin solution, and 

 with fresh and used water-formalin solution (Table 5), As will be 

 seen, there was not much difference in the results between the fresh 

 and used solutions. It was clearly indicated, however, that there 

 was a great variation in the rapidity with which the solutions passed 

 throu^ the various cappings. 



Twenty cappings were tested in the alcohol-formalin solution. 

 In 5 cases no solution passed through the cappings within the five- 

 minute period ; in 6 cases the liquid in the tube rose 1 centimeter or 

 less; in 2 cases it rose between 1 centimeter and 2 centimeters; in 4 

 cases there was a rise of between 2 centimeters and 3 centimeters ; and 

 in 3 cases the liquid rose to the 3 centimeter mark in less than five 

 minutes. Twenty cappings were likewise tested in the water-for- 

 malin solution. In 9 cases no solution passed through the cappings 

 in periods varying from 5 to 10 minutes, and, in 1 case, even 60 

 minutes ; in 4 cases there was a rise of liquid in the tube of 1 centi- 

 meter or less, one of these after 10 minutes ; there were 3 cases of a rise 



