2l6 BACTERIOLOGY. 



Bacillus icteroides grows readily upon the ordinary nutritive media 

 fluid and solid. It is described as a rod about 2^-4^ in length, with 

 rounded ends, often joined in pairs, and staining readily with the 

 ordinary aniline dyes, but decolorized by Gram's method. The 

 colonies upon a gelatin plate resemble in some particulars those of 

 the colon bacillus, but never show any trace of the chestnut color 

 developed in cultures of the latter ; so-called pleomorphism of the 

 colonies is, however, marked. 



Contrary to what is true of -most of the known pathogenic mi- 

 crobes, the growth of B. icteroides upon agar is especially character- 

 istic and furnishes a diagnostic test of the first importance. If the 

 cultures are allowed to develop in the incubator at 37 for from 12 

 to 24 hours, and are then transferred to a temperature of from 20 

 to 28, there is produced what Sanarelli regards as a highly charac- 

 teristic appearance. The growth at the lower temperature forms a 

 sort of halo around the portion of the colony developed in the incu- 

 bator, and this appearance is so singular that according to Sanarelli 

 a mere superficial inspection suffices to distinguish immediately, and 

 with the naked eye, a colony of B. icteroides in the midst of all other 

 bacterial colonies yet described. As the growth goes on, an effect 

 is produced as if a layer of opaque paraffin had been poured over the 

 agar and then impressions made in it with a small circular seal, the 

 imprints of this seal corresponding with the original transparent 

 colonies grown in the incubator. The final aspect of the culture is 

 compared to a miniature archipelago in which the islets would be 

 represented by the colonies first developed, and the surface of the 

 water by the layer subsequently formed at the lower temperature. 



Blood-serum and potato proved themselves to be rather unsuit- 

 able media for B. icteroides. In milk the germ grows readily, but 

 without producing coagulation. The most favorable fluid medium 

 tejsted by Sanarelli was beef broth containing lactose and calcium 

 carbonate. 



The germ is pathogenic for most of the domestic animals. Mice, 

 guinea-pigs and rabbits succumb readily to inoculation with a pure 

 culture. -The rabbit is considered as the most favorable subject for 

 experimental inoculation, and possesses notable advantages over the 

 guinea-pig both in susceptibility and in the regularity and constancy 

 of symptoms and death. The dog, however, presents the most in- 

 structive instance of close analogy with yellow fever as manifested in 

 man. Both in the symptoms and in the anatomical lesions Sanarelli 

 was able to trace a correspondence at once constant and precise. 

 As is the case in man, the liver and the kidneys are the organs es- 



