STAPHYLOCOCCUS PYOGENES AUREUS 399 



the tetrads are slightly larger in size than the ordinary staphylo- 

 coccus, flattened along their adjacent surfaces, and surrounded by 

 a thick halo-like capsule. Preparations from cultures often lack 

 these capsules. The micrococcus is easily stained by the usual basic 

 aniliii dyes. Stained by Gram's method, it is not decolorized, retain- 

 ing the gentian-violet. 



Cultivation. Micrococcus tetrageiius grows on the ordinary 

 laboratory media, showing a rather more delicate growth than do 

 the staphylococci. 



On agar, the colonies are at first transparent, later they become 

 grayish-white, but are always more transparent than are staphylo- 

 coccus cultures. 



On gelatin, growth is rather slow and no liquefaction takes place. 



Broth is evenly clouded. 



On potato there is a white, moist growth which shows a tendency 

 to confluence. 



Milk is coagulated and litmus milk indicates acid formation. 



Pathogenicity. Micrococcus tetragenus is especially pathogenic 

 for Japanese mice, which succumb within three or four days to sub- 

 cutaneous inoculation. 43 Gray mice, rats, guinea-pigs, and rabbits 

 are less susceptible, showing only a localized reaction at the point 

 of inoculation. The organism has occasionally been isolated from 

 spontaneous abscesses observed in domestic animals. 



In man, this microorganism is usually found without any par- 

 ticular pathogenic significance, in sputum or saliva. In isolated 

 cases, however, it has been described as the sole incitant of abscesses. 



Bezanc.on 44 has isolated Micrococcus tetragenus from a case of 

 meningitis. A single case of tetragenus septicemia is on record, 

 reported in 1905 by Forneaca. 45 



In America, this microorganism has not been frequently observed 

 in connection with disease. It is often found, however, in consider- 

 able numbers, in smears of sputum which are being examined for 

 pneumococci or tubercle bacilli. 



ENTEROCOCCUS. This is a capsulated streptococcus found fre- 

 quently in the intestines of infants, and first described by Escherich 

 and Tavel. It is a pleomorphic organism which may appear in the 



"Miiller. Wien. klin. Woch., 17, 1904. 



44 Bezan^on, Semaine mod., 1898. 



45 Forneaca, Rif. med., 1903. 



