CHAPTER XLV. 

 MICROCOCCUS TETRAGENUS. 



Introduction. 



Section I. Experimental inoculation, p. 631. 



Section II. Morphology, p. 632. 



Section III. Biological properties, p. 632. 



Section IV. Detection, isolation and identification of the organism, p. 633. 



THE Micrococcus tetragenus was first noticed by Koch in some pus from a 

 cavity in the lung. The characteristics of the organism were studied by 

 Gaffky. 



The Micrococcus tetragenus is very commonly present on the skin and is found 

 also in the saliva, stomach and nasal mucus of healthy persons. Outside the body 

 it occurs as a saprophyte and is often found in the air. Under certain conditions 

 it may become pathogenic : it is frequently associated with the tubercle bacillus 

 in tuberculosis of the lung, in some oases it is the cause of sore throat (" angines 

 sableuses " of Dieulafoy and Appert), sometimes of suppuration in very various 

 parts of the body (purulent pleurisy, adenitis, meningitis, dental abscess, furuncu- 

 Josis, etc.) and occasionally of septicaemia. 



SECTION I. EXPERIMENTAL INOCULATION. 



As in the case of the staphylococci the virulence of the Micrococcus tetragenus 

 is very variable. For purposes of experimental inoculation a virulent strain 

 must be used. 



Mice. White mice are very susceptible. A few drops of a broth culture 

 inoculated beneath the skin leads to death from septicaemia in 24-48 hours ; 

 the blood and internal organs will be found to contain numerous tetrads. 



Guinea-pigs. In guinea-pigs, sub-cutaneous inoculation is followed by the 

 formation of an abscess containing thick pus : death may occur in 3-5 days, 

 but as a rule the disease is less acute. Intra-peritoneal inoculation is a 

 more severe mode of infection than the sub-cutaneous method and leads to 

 a fatal result in a few days : post mortem a purulent effusion will be found in 

 the peritoneal cavity and the organism can be isolated from the blood and 

 internal organs. 



Rabbits. Rabbits are less susceptible. Sub-cutaneous inoculation leads 

 to the formation of a cold abscess (Tissier) while intra-peritoneal inoculation 

 is followed by peritonitis with a collection of thick pus in the peritoneal 

 cavity. 



