MICROCOCCUS TETRAGENUS 207 



obtained to it; in fact, in its properties it presents a close 

 analogy to the ■ toxins of diphtheria and tetanus. The two 

 staphylococci mentioned also produce a toxin which kills 

 leucocytes, and is therefore called " leucocidin " (van de Velde). 

 This toxin can be obtained by nitration of fluid cultures, and 

 on being injected into animals leads to the formation of an 

 antitoxin. Apparently the same leucocidin is produced by the 

 staphylococcus aureus and staphylococcus albus. 



Micrococcus 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. 48), and is thus generally found in the tissues in groups 

 of four, or tetrads, which are 

 often seen to be surrounded by ,.-•— 



a capsule. The cocci measure 



1 p. in diameter. They stain ^* 



readily with all the ordinary / 5 Jf 



stains, and also retain the .* u, ';- £ -. 



stain in Gram's' method. ,-' * i 



It grows readily on all the I « JC . { ■'•,'■■•'■» % 



media at the room tempera- J ▼ ♦ * * \ 



ture. In a puncture culture .■"'■.'£* *. i 



on peptone-gelatin a pretty ■ „. * f * J 



thick whitish line forms along 

 the track of the needle, whilst 

 on the surface there .is a 

 thick rounded disc of whitish 



the track of the needle, whilst \ * ft 



on the surface there is a ' * <rC 



colour. The gelatin is not ^ M , 



liquefied. On the surface of * ^ 



agar and of potato the growth * * *~ 



is an abundant moist layer of * _l~-^ 



the same colour. The growth 



on all the media has a peculiar Fig. 48.— Micrococcus tetragenus ; young 



viscid or tenacious character, _ . culture on agar, showing tetrads 



owing to the gelatinouscharac- Stamed wlth weak carbol-fuehsm. x 1000. 



tef of the sheaths of the cocci. 



White mice are exceedingly susceptible to this organism. Subcutaneous 

 injection is followed by a general septicaemia, the organism being found 

 in large numbers in the blood throughout the body. Guinea-pigs are 

 less susceptible ; sometimes only a local abscess with a good deal of 

 necrotic change results ; sometimes there is also septicaemia. 



Bacillus coli communis. — The microscopic and cultural characters are 

 described in the chapter on Typhoid Fever. The bacillus lactis aerogenes 

 and the bacillus pyogenes foetidus closely resemble it ; they are either 

 varieties or closely related species. The former is distinguished by 

 producing more abundant gas formation, and by its growth on gelatin, 

 etc., being thicker and whiter than that of the bacillus coli. 



Bacillus proteus. — The term proteus has been applied to a group of 

 Intestinal bacteria, of which several varieties have been described, e.g., 

 vulgaris, mirabilis, zenkeri, capsulatus; the "urobacillus septicus" is 

 also a variety of proteus. They are characterised by their pleomorphism, 

 hence the name, and by the rapid liquefaction of gelatin which they 

 produce. Proteus vulgaris has the following characters : It is a small 



