SACBROOD. 31 



AMOUNT OF VIRUS REQUIRED TO PRODUCE THE DISEASE, AND THE 

 RAPIDITY OF ITS INCREASE, 



Assuming the virus of sacbrood to be a very minute microorgan- 

 ism, the number of germs present in a larva dying of the disease must 

 be considered as exceedingly large. Whether a single germ taken 

 up by a larva will produce the disease in every instance, or in any 

 instance, is not known. If the disease does result at any time from the 

 ingestion of a single germ, ail of the conditions, it may be assumed, 

 must be especially favorable for the production of the disease. From 

 what is known of diseases of other animals and of man, and from the 

 results thus far obtained in the study of sacbrood, it is well, at present, 

 to assume that the number of sacbrood germs taken up by a larva 

 may be so small that no disease results. 



It is certain, however, that a comparatively small number of 

 sacbrood germs ingested by a larva about two days old are sufficient to 

 produce the disease. That the few germs thus taken up can increase 

 within the larva during an incubation period of five or six days to 

 such a vast number as is assumed to be present in a larva dying of 

 the disease indicates the extreme rapidity with which the germs are 

 able to multiply. 



The minimum quantity of virus necessary to produce a moderate 

 infection in a colony has not been definitely determined. It was 

 found by experiments, however, that the virus contained in a single 

 larva recently dead of the disease was sufficient to produce a large 

 amount of sacbrood in a colony. 



As a very rough estimate, it may be said that the quantity of virus 

 in a single larva dead of sacbrood is sufficient, when suspended in 

 half a pint of sirup and fed to a healthy colony, to produce in- 

 fection in and death of at least 3,000 larvae. Starting then with the 

 virus contained in a single larva, in less than one week it would 

 easily be possible to have 3,000 larvae dead of the disease, which 

 means that the virus has been increased 3,000-fold within one week. 

 This latter amount of virus would be sufficient to produce an equal 

 amount of infection in 3,000 colonies, increasing the amount of virus 

 again 3,000-fold. In less than two weeks, therefore, theoretically 

 it would be possible to produce a sufficient amount of virus to infect 

 9,000,000 colonies, more colonies probably than are to be found at 

 present in the United States. Carrying the idea somewhat further, 

 within three weeks, theoretically enough virus could be produced 

 to inoculate every colony in existence. 



These facts are sufficient to indicate somewhat the enormous 

 rapidity with which the virus of sacbrood is capable of increasing. 



