22 Department Circular 28b, U. S. Dcpt. of Agriculture 



combs infected with American foulbrood by means of various for- 

 maldehyde disinfectant solutions as used by beekeepers. It was 

 found to be true even with solutions of low surface tension and sup- 

 posedly good penetration, such as alcohol-formalin solution, as 

 well as with solutions having high wetting and spreading powers 

 with regard to waxy surfaces, such as soap-formalin solutions. In 

 all of the several series of combs treated, even after a treatment of 

 48 hours, cultures from varying numbers of scales from capped cells 

 gave growths of Bacillus larvae. A comparison of the percentage 

 of sealed cells not sterilized indicates that the efficiency of the alco- 

 hol-formalin solution is relatively no greater in this regard than 

 that of water-formalin solution. 



The explanation of this failure of the formaldehyde disinfectants 

 to sterilize all the sealed brood may be found in the varying per- 

 meability of the brood cappings, particularly many of those cover- 

 ing remains of American foulbrood. In some cases no solution was 

 able to pass through the cappings, low surface tension of the liquid 

 and solvent action on the wax seeming to be ineffective factors. In 

 these cases the glue-like remains of diseased dead larvae have often 

 become smeared over the inner surface of the cappings during the 

 routine handling of the combs, drying there and clogging the pores 

 of the cappings. As a result, no solution could penetrate them, at 

 least within a length of time practicable for treating combs with- 

 out subjecting them to action causing undesirable deterioration. 

 Even on the same comb there is wide variation in the structure of 

 the cappings themselves. As can be noted in the various tables, 

 there is great irregularity as to which comb of a series shows the 

 first sealed cells giving a growth of Bacillus larvae, indicating in- 

 complete sterilization. The experiments with glass cells indicate the 

 possibility that the complete sterilization achieved in many of the 

 sealed cells is brought about by the penetration into the cells of 

 formaldehyde gas and water vapor liberated from the disinfectant 

 solution, rather than by actual liquid sufficient to cause sterilization. 

 Experiments with the use of a vacuum in treating combs indicated 

 that relatively little solution enters the majority of sealed cells at 

 usual atmospheric pressure, but that the method should be effective 

 with all uncapped cells. These facts may explain the few cases of re- 

 currence of disease so far noted with the method now in use, and serve 

 as the basis of a prediction of more cases in the future. Why more 

 such recurrences have not been observed is not easy to explain, but 

 it is to be remembered that this method of disinfecting combs has 

 been in use for only about two } T ears and much concerning it is yet 

 to be learned. 



A certain proportion of the cultures of scales from sealed cells 

 (25 per cent of those treated with alcohol-formalin solution and 

 about 33 per cent of those treated with water-formalin solution) 

 showed comparatively few germinated spores. In some of these 

 cases no growth was visible on the surface of the culture medium. 

 Some few of these cultures on subculturing failed to show further 

 growth or germination. The question here arises whether contact 

 with formaldehyde insufficient to kill may lower the vitality of these 

 organisms so that they fail to continue growth, or may lower their 

 virulence, thereby inhibiting infection of healthy colonies from such 

 sources. It is also possible that an insufficient number of spores 



