598 THE STREPTOCOCCI OF MAN 



Some streptococci, however, and especially the short chain forms produce a turbid 

 growth after incubating for 24 hours at 37 C. : later finely granular masses appear 

 in the medium and these after 3-5 days' growth fall to the bottom leaving the 

 medium clear. 



[Aronson uses glucose-broth for growing streptococci] : and according to 

 Ucke, 5 per cent, glycerin-broth is a very useful medium for the growth of 

 the organism. 



Marmorek's phenomenon. If a broth culture of a streptococcus be filtered 

 and the filtrate be then resown either with the same or with another strain 

 of streptococcus the organism fails to grow while any other organism, e.g. a 

 staphylococcus, a pneumococcus, etc., will grow abundantly. This failure to 

 grow in a filtered broth culture is common to all streptococci found in human 

 disease processes ; it is to be noted, however, that streptococci isolated from 

 cases of scarlet fever may give a very poor growth. The streptococcus of 

 strangles (Chap. XLII.) can, by means of this test, be readily distinguished 

 from all other streptococci : in a streptococcal filtrate this organism grows 

 almost as well as any other organism. Marmorek quotes this experiment 

 as a valuable argument in favour of his view that all streptococci of human 

 origin are identical. 



Liquid seriim. Fresh rabbit serum is a very favourable culture medium, 

 but ascitic fluid and bovine and horse serum alone, without any addition, 

 are not particularly useful ; the growth on the latter media is poorer than in 

 broth but otherwise has similar characteristics. 



Serum-broth and blood-broth. Marmorek recommends the following media 

 as giving rich and virulent cultures. 



(a) Equal parts of peptone-broth and human serum. The best. 



(/?) Equal parts of peptone-broth and ascitic or pleural fluid. 



(y) One part of peptone-broth and two parts of horse, mule, or donkey 

 serum. 



The characteristics of the growth are similar to those on broth. 



[Besredka keeps his stock cultures of streptococci in a mixture consisting of 

 equal parts of Martin's broth and heated (56 C. for ^ hour) horse serum. This 

 observer finds that the organisms remain alive hi this medium for a long time and 

 retain their virulence well.] 



Milk. When streptococci are grown in milk the medium is coagulated 

 usually after 4 or 5 days, occasionally later. In some cases no clot is formed. 

 [Andrewes and Horder found that among the streptococci pathogenic for man 

 studied by them, the commonest, which they describe as S. pyogenes, does 

 not coagulate milk. On the other hand those which they refer to the groups 

 S. salivarius, S. anginosus, S. fcecalis all produce clot in milk (vide infra]. 

 Schottmiiller's Streptococcus pyogenes does not clot milk. ] 



Gelatin. The growth in gelatin stab culture is poor and consists of isolated, 

 circular, opaque-white colonies barely the size of a pin's head. Growth 

 ceases about the fifth day and the organisms soon die. [As already pointed 

 out some streptococci do not grow at all at the temperature of solid gelatin, 

 20 C.] 



[As a rule] the medium is not liquefied. [Andrewes and Horder, however, 

 isolated a few pathogenic streptococci which liquefied gelatin. S. fcecalis 

 (vide infra] liquefies gelatin far more commonly than S. pyogenes.] 



Agar. After incubating for 12-24 hours at 37 C. a number of small whitish 

 colonies, resembling grains of semolina, appear along the line of sowing. On 

 further incubation the colonies increase in size, and may become confluent 

 forming a somewhat thin, semi-opaque, greyish band with more or less sharply 

 defined edges. The culture soon dies out. 



