152 Empusa Miiscae versus Musca Domestica L. 



When, through the courtesy of Dr. C. Gordon Hewitt, some original 

 material of Mr Hesse's culture was placed at my disposal, I could, 

 on examination, find nothing else but Mucor racemosus, which certainly 

 produced after a few days a luxuriant growth of the same fungus : we 

 also observed "spores," but not Em/pusa spores. Since that time 

 experiments have been made with spores of this universal mould fungus 

 on living flies, but, notwithstanding an ample supply cjuite sufficient 

 to fatten them, they died of starvation; but under no circumstances 

 was death due to Mucor racemosus, since sound flies, kept under iden- 

 tical conditions minus the fungus, died about the same time from the 

 effects of confinement. Mr Hesse solved the difficulty apparent in 

 this instance by concluding that this fungus was polymorphic, and 

 "that Empusa was merely a parasitic form of the Mucor." Mr Hesse 

 supplements this statement by the following paragraph: — 



"The idea that the Empusa Muscae might be polymorphic now 

 presented itself, and also that this might be the reason that its culti- 

 vation had not apparently been successful hitherto. I reaUsed that 

 one should not expect to produce a purely parasitic growth on a dead 

 medium (sic!), but that, as in the case of other fungi when artificially 

 cultivated, a morphological change might be expected; and came to 

 the conclusion that Mucor racemosus, although a saprophyte, might, 

 when the spore is ingested by the fly, assume a parasitic existence 

 and produce the growth, in the tissues of the fly, known as Empusa 

 Muscae, whose spores, when cultivated on artificial media, revert to 

 the saprophytic stage." 



It is regrettable to notice the author's attempt to interpret an error 

 of his by proposing a somewhat fantastic theory. Surely before such 

 explanation is necessary, he should be sure that what he recorded 

 as occurring did actually occur, viz. : the growth of Mucor from ger- 

 minating Empusa spores. It is so clear that it hardly needs stating 

 that he has confused an adulteration of his "cultures" with what he 

 thought he had produced. The use of an egg yolk medium "in thin 

 layers in a Petri dish, sterilised by steam at 100° C. for one hour on three 

 days in succession," clearly indicates the degree of importance attaching 

 to the author's further results, whatever they may be. 



He proceeds then by inserting bodies of flies which had died of 

 Empusa during the previous autumn. Control dishes were also pre- 

 pared. In five days sporangia had formed on the dishes containing 

 the egg medium, whilst the control dishes remained quite sterile. The 

 author, unfortunately, does not indicate whether he placed on his 



