I 



H. T. GtJssow 155 



may now be somewhat loosely called Mucor racemosus, was readily 

 secured from the bodies of any dead fly. We cannot, of course, doubt 

 the correctness of the recorded observations ; but we are of the opinion 

 that if a Mucor proved fatal to flies in the manner described in these 

 experiments, it must have been one of the pathogenic types or a different 

 species altogether. We expect close diagnostic studies of the patho- 

 genic organism would soon establish the identity. But we do absolutely 

 question that Mucor developes from an uncontaminated Empusa spore. 

 We are glad to note that Mr Ramsbottom has now become interested 

 in clearing up this somewhat involved research work; and we quite 

 agree with him that — if Mr Hesse's assumption is correct that Empusa 

 is a polymorph — a fundamental biological principle would be absolutely 

 overthrown. 



The critic, tkey say, but assumes the role when he has failed in 

 producing good or marketable merchandise in his own hne. That I have 

 assumed the critic's role, I may not deny: in w^hat follows, I would 

 play a constructive part, with what success I modestly leave in turn 

 to my critics to say. 



I wish, therefore, in concluding to record some of my cultural ex- 

 periences and other observations on Empusa Muscae, which I have 

 not hitherto published. This may assist in simphfying the apparent 

 difficulties which Mr Hesse had in securing an uncontaminated growth 

 from Empusa spores. 



In my last paper (loc. cil.) I described briefly a method of successful 

 auto-infection of flies coming into contact with flies recently dead from 

 Empusa. By this means one has under one's own control the securing 

 of fresh material of the fungus for a considerable period. By placing 

 a fly showing the fresh belts of fungus growth on a pillar made of plas- 

 ticine, this latter can be bent and twisted under the microscope into 

 any position. When carefully adjusted one can observe the discharge 

 of spores very readily. These fly in every direction and for distances 

 of about seven centimetres. 



Hence this fact was used for obtaining spore cultures quite easily, 

 and uncontaminated. A series of clear coverglasses was placed at the 

 bottom of a sterile jar, which was closed with an ordinary cork. A fly 

 which was observed to be surely "infected" — experience having shown 

 the incipient symptoms of infection, viz. sluggishness, increase in volume 

 and lightening in colour of abdomen, and a peculiar reddish colour, 

 a dirty brick red, of tTie " eyes" — was pinned on to the cork from below, 

 so that, when the stopper was replaced, the fly was securely held above 



