330 THE BEGINNINGS OF LIFE. 



In its epidemic form, muscardine is most prone to 

 occur at the season when the worms are just about to 

 pass into the chrysalis condition. At this critical 

 period, unknown influences are apt to operate upon 

 them which produce abnormal and specific nutritional 

 changes ; and then the disease breaks out like a pesti- 

 lence, attacking almost all the worms of a given 

 locality. 



Again, it is well known that the growth of a mould 

 (Empusa) frequently seems to prove fatal to flies in 

 autumn ] . This subject has been investigated by 

 Professor Cohn, who came to the opinion that the 

 parasitic growth commenced by an independent de- 

 velopment of Fungus-germs in the blood of the sickly 

 animal. He does not believe that the disease is incited 

 by the mysterious introduction of Fungus-germs into 

 their circulating system from without. He sums up by 

 saying ( c Hedwigia, J 1855, p. 59) that c the influence of 

 the spores of Empusa in the appearance of this fungus, 

 and of the disease in flies, is by no means evident, since 

 the genesis, the chemical and optical characters of the 

 numberless free cells in the blood, the absence of a 

 special expanded mycelium, and, above all, the whole 



de la muscardine une foule d'individus echappent, non pas a transmission, 

 ainsi qu'on le dit, mais bien au developpement des spores. Voila pour- 

 quoi beaucoup d'observateurs ont conteste la transmissibilit^ de la 

 Muscardine d'un individu a un autre.' ('Veg^taux Parasites,' 1853, 



p. 582-) 



1 This mould will always appear on a dead fly which is allowed to 

 float for a few days on the surface of water. 



