STAPHYLOCOCCUS, PYOGENES CITREUS 333 



A large number of staphylococci, differing from those described 

 above in one or another detail, have been observed. They are of com- 

 mon occurrence and are met with chiefly as contaminations in the course 

 of bacteriological work. Few of these have any pathological significance 

 and none of them are toxin-producers, so far as we know. Many of them 

 differ, furthermore, in their inability to liquefy gelatin. All of them 

 belong more strictly to the field of botany than to that of patho- 

 logical bacteriology. 



Atypical pathogenic staphylococci have been described by a number 

 of observers. Thus Weichselbaum * isolated a staphylococcus from a 

 case of malignant endocarditis which could not be cultivated at room 

 temperature, and grew only in very delicate colonies. Veillon, 2 moreover, 

 has described a strictly anaerobic staphylococcus cultivated from the 

 pus of an intra-abdominal abscess. 



MICROCOCCUS TETRAGENUS 



In 1881, Gaffky 3 discovered a micrococcus which occurs regularly 

 in groups of four or tetrads. He first isolated it from the pus discharged 

 by tuberculous patients with pulmonary lesions. Observed in smear 

 preparations from pus, the tetrads are slightly larger in size than the 

 ordinary staphylococcus, 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 anilin dyes. Stained by Gram's method, it is not decolor- 

 ized, retaining the gentian-violet. 



Cultivation. Micrococcus tetragenus grows on the ordinary labora- 

 tory media, showing a rather more delicate growth than do the staphy- 

 lococci. 



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

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

 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. 



1 Weichselbaum, Baumgarten Jahresb., 1899, Ref. 



2 Veillon, Compt. rend. soc. de biol., 1893. 



a Gaffky, Mitteil. a. d. kais. Gesundheitsamt, i, 1881. 



