10 BULLETIN 180, U. S. DEPABTMBNT OF AGBICULTUEE. 



always necessary to establish the causal relationshii) between the 



eerm and the disease. . , 



Because of the absence of any of the higher animal parasites and 

 of fungi in bees suffering from Nosema-disease these groups ot para- 

 sites naturally can be eliminated as possible causal factors Maiden 

 (1912 1913) studied the bacteriology of Nosema-infected bees. Me 

 found that the number of bacteria in the diseased bees was much 

 greater than in normal ones, the proportion being as 12 to l._ He 

 found howeyer, no evidence of a direct etiological relation existmg 

 between these bacteria and the disease. Whether they play a 

 secondary r61e is a question which admits of much discussion but 

 one which is somewhat foreign to the present paper. 



Some preliminary experiments were made by the writer m regard 

 to the possibmty of the presence of a filtrable virus m Nosema- 

 disease. The results obtained mdicate that no such virus is present. 

 By thus eliminating, at least tentatively, the higher animal para- 

 sites, the fungi, the bacteria, and the filtrable viruses— groups of 

 parasites which cause diseases m animals— there remains another 

 group, the protozoa. Of this group there is only one species, Nosewi, 

 apis, that is constantly present in Nosema-disease. Other protozoa 

 are occasionally encountered in adult bees, but when found are 

 present usually in small numbers only. The conclusion is naturally 

 reached, therefore, that Nosema apis is the cause of Nosema-diseasei 

 Such a conclusion is in harmony with views generally accepted at the 

 present time in regard to proof necessary to establish the causal re- 

 lation of such a germ to the disease. 



PREDISPOSING CAUSES. 



Experimental inoculations have shown that in general adult bees 

 of all ages are susceptible to Nosema infection. In nature it is found 

 that the youngest bees are always free from infection and that the 

 old shiny bees usually are. The absence of Nosema apis in the younger 

 ones may be attributed simply to the fact that they have not yet been 

 infected through the taking of food containing the germ. In the case 

 of the shiny bees it seems probable that they have escaped infection, 

 although it is possible that some of them might have been infected 

 at one time and later recovered. "-^ 



The brood does not seem to be at all susceptible to infection with 

 Nosema apis. In heavily infected colonies the larvae and pupae appar- 

 ently remain healthy. In these studies larvae were inoculated more 

 or less directly by means of a pipette and examinations * were made 

 daily following the inoculation. The spores were found m.ixed with 



> The examinations were made througli fixing and sectioning inoculated larvae. 



