MICROCOCCUS 7ETRAGENUS. 171 



liquefaction. Around the colonies a greenish tint appears. On agar 

 the growth forms an abundant slimy greyish layer which afterwards 

 becomes greenish, and a bright green colour diffuses through the 

 whole substance of the medium. On potatoes the growth is an 

 abundant reddish -brown layer resembling closely that of the glanders 

 bacillus, and the potato sometimes shows a greenish discoloration. 



From the cultures there can be extracted by chloroform a coloured 

 body pyocyanin, which belongs to the aromatic series, and crystallises in 

 the form of long, delicate bluish-green needles. On the addition of a 

 weak acid its colour changes to a red. 



This organism has distinct pathogenic action in certain animals. 

 Subcutaneous injection of small doses in rabbits may produce a local 

 suppuration, but if the dose be large, spreading hsemorrhagic oedema 

 results, which may be attended by a septicaemia, the organism occurring 

 throughout the body. Intravenous injection may produce, according 

 to the dose, rapid septicaemia with nephritis, or sometimes a more 

 chronic condition of wasting attended by albuminuria. 



Microccocus Tetragenus. This organism, first described by Gaffky, 

 is characterised by the fact that it divides in two planes at right angles 

 to one. another (Fig. 49), 

 and is thus generally found 

 in the tissues in groups of 

 four or tetrads, which are 

 oft en seen to be surrounded & ftft 

 by a capsule which stains J ^ * { 



faintly or not at all. The * * i * * * 



cocci measure I p. in dia- 4 



meter. They stain readily * . 



with all the ordinary ^ * 



stains, and also retain '' * f \t 



the stain in Gram's . 



method. f 



It grows readily on all + - 



the media at the room * * 



temperature. In a punc- * v % 



ture culture on peptone- 

 gelatine a pretty thick 



whitish line forms along FIG. 49. Micrococcus tetragenus ; young 

 the track of the needle, culture on agar, showing tetrads, 

 whilst on the surface there Stained with weak carbol-fuchsin. x 1000. 

 is a thick rounded disc 



of whitish-yellow colour. The gelatine is not liquefied. The colonies 

 in gelatine plates are rounded yellowish-white points, which under 

 a low power show a granular or slightly nodulated surface ; the super- 

 ficial colonies appear as opaque round drops of yellowish-white colour. 

 On the surface of agar and of potato the growth is an abundant moist 

 layer of the same colour. The growth on all the media has a peculiar 



