H. T. GiJssow 151 



the substratum where it died. In the locaUties referred to, many- 

 thousands of flies frequented the places daily, but only from 1 to 4 at 

 the most of newly deceased flies' bodies were observed on any one day 

 during a period of 22 days. Hence in nature this fungus does not 

 appear to account for the general disappearance of flies in winter. 



Though I am quite satisfied that one cannot speak of this disease 

 as the cause of an epidemic among flies, and though, endemically, it 

 may be present every season, the fact that it is so fatal to individual 

 flies made it desirable to experiment with the fungus with a view to 

 spreading the disease more widely and rapidly. This might be done 

 were it possible to grow the fungus conveniently in artificial culture, 

 and use it in the manner of, for instance, D'Herelle's Goccobacillus 

 acridiorum, pathogenic to grasshoppers. 



Methods of securing artificial cultures h^ive been tried by a number 

 of observers, and because of some recent pubhcations on the subject, 

 which, perhaps, have not come to the attention of scientific workers, 

 it will not be out of place to discuss the opinion of these writers here. 

 In the last note which I prepared (loc. cil.), I briefly dealt with the 

 investigations of Mr Edgar Hesse, on the subject of culture of Em/pusa. 



The seventh report of the same Board (No. 102, 1914) contains 

 further contributions to the subject under discussion. In the letter 

 of transmittal Dr Newsholme, the medical ofl&cer of the Board, briefly 

 reviews the original contributions in the report. We now take excep- 

 tion to the statement that the Empusa "is known to be the cause of 

 much of the mortahty among the house flies during the autumn months," 

 because of careful observations on the rate of mortahty. Notwith- 

 standing my friendly criticism of Mr Hesse's 1912 work in the sixth 

 report, his work receives much support from Dr Bernstein who 

 was appointed by the Board "to supervise and control Mr Hesse's 

 investigations." It mu^st be pointed out here that Mr Hesse claimed 

 and "proved" (!) "the possibility of obtaining from spores of E. Muscae 

 derived from flies which had died of the disease, a culture which, under 

 suitable conditions as to moisture and food material, gave a luxuriant 

 growth in a few days, followed by the production of spores. These 

 spores when mixed with syrup and fed to normal flies, induced in them 

 a rapidly fatal disease, which, as judged by the naked eye and by 

 microscopical examination, was indistinguishable from the disease 

 found in the flies attacked by Emjmsa Muscae in the ordinary course." 

 Mr Hesse, be it noted, refers to luxuriant growth and production of 

 spores, but does not here state what growth or spores. 



