MICROCOCCUS TETRAGENUS. 1 87 



twenty-four hours, and at its upper part a small cup of liquefaction forms 

 within forty-eight hours. At this time a slightly greenish tint is seen in the 

 superficial part of the gelatin. The liquefaction extends pretty rapidly, the 

 fluid portion being turbid and showing masses of growth at its lower part. 

 The green colour becomes more and more marked and diffuses through the 

 gelatin. Ultimately liquefaction reaches the wall of the tube. In plate cul- 

 tures the colonies appear as minute whitish points, those in the surface being 

 the larger. Under a low power of the microscope they have a brownish yel- 

 low colour and show a modulated surface, the superficial colonies being thinner 

 and larger. Liquefaction soon occurs, the colonies on the surface forming 

 shallow cups with small irregular masses of growth at the bottom, the deep 

 colonies small spheres of liquefaction. Around the colonies a greenish tint 

 appears. On agar the growth forms an abundant slimy greyish layer which 

 afterwards becomes greenish and has a metallic sheen, and a bright green 

 colour diffuses through the whole substance of the medium. On potatoes the 

 growth is an abundant reddish-brown layer resembling that of the glanders 

 bacillus, and the potato sometimes shows a greenish discoloration. Milk is 

 slightly acidified, and peptonised without coagulation as a rule. 



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 r 



In man, many observers have described it as being associated with 

 abscess formation, pericarditis, pyelitis, dysentery, etc. It has likewise dis- 

 tinct pathogenic action in certain animals. Subcutaneous injection of small 

 doses in rabbits may produce a local suppuration, but if the dose be large, 

 spreading haemorrhagic oedema results, which may be attended by septicaemia. 



Intravenous injection may pro- 

 duce, according to the dose, rapid 

 septicaemia with nephritis, or some- 

 times a more chronic condition of ^ w v 

 wasting attended by albuminuria. ? * 



Micrococcus tetragenus. This & 



organism, first described by Gaffky, % t 



is characterised by the fact that it Si * 



divides in two planes at right angles f * 

 to one another (Fig. 70), and is thus ., 



generally found in the tissues in groups f 



of four or tetrads, which are often m f 



seen to be surrounded by a capsule. + fr * 



The cocci measure i //, in diameter. <l 



They stain readily with all the ordi- 

 nary stains, and also retain the stain FIG. 70. Micrococcus tetragenus; young 

 in rViv'o * , *i A culture on agar, showing tetrads. 



m Gram s method. Stained ^ weak carbol . fuchsin . x Iocxx 



It grows readily on all the media 



at the room temperature. In a puncture culture on peptone-gelatin a pretty 

 thick whitish line forms along the track of the needle, whilst on the surface 

 there is a thick rounded disc of whitish colour. The gelatin is not liquefied. 



