1897J MICROSCOPICAL JOURNAL. 325 



reflections; that is to say, they are completely distinct 

 from those grown in the incubator. 



These different modes of evolution can be used for 

 diagnosis by exposing cultures, first, for from twelve to 

 sixteen hours to the temperature of the incubator, and 

 afterward for other twelve to sixteen hours to the temper- 

 ature of the air. 



This done, the colonies show themselves to be con- 

 structed with a flat central nucleus, transparent and 

 azure, having a peripheral circle prominent and opaque. 

 This peculiarity, which may be considered specific, may 

 be made evident in less than twenty-four hours, serving 

 thus to establish the bacteriological diagnosis of the 

 "bacillus icteroides." 



Apart from this morphological characteristic, which 

 suffices of itself to differentiate the microbe of yellow 

 fever from all others previously known, the "bacillus 

 icteroides" is endowed with some interesting biological 

 qualities. 



It is a facultative anaerobe, and does not resist the 

 Grram stain ; it ferments insensibly lactose, more actively 

 glucose and saccharose, but is unable to coagulate milk; 

 it does not produce iudol, and is very resistant to drying; 

 it dies in water at 60° C. or after being exposed for seven 

 hours to the solar rays, and lives for a lon^ time in sea 

 water. 



The microbe of yellow fever is pathogenic for the 

 greater number of the domestic animals. Few microbes 

 have a pathological dominion so extended and so varied. 

 Birds are completely refractory, but all the raammiferous 

 animals upon which I have experimented have shown 

 themselves more or less susceptible. 



But of all the animals, that which lends itself best to 

 showing the close analogy, anatomically and nosologi- 

 cally, between experimental yellow fever and human yel- 

 low fever, is the dog. 



