452 HILDA HEMPL HELLER 



good, meat medium not neutralized in the making is also good. 

 Ordinary meat medium, the culture being taken early in its de- 

 velopment, is usually sufficiently selective. Sugar media selective 

 for certain groups may be used, if the number of cultures to be iso- 

 lated warrants the investigation of the sugars split by that group. 

 I have found that culture in casein-digest liver-broth renders black- 

 leg the most able guinea-pig invader in ablackleg-vibrion-septique 

 mixture. To increase the percentage of proteolytic organisms use 

 meat medium or brain medium in a culture two to four days old, or 

 even older; or employ the medium of Achalme-Passini, salt solution 

 or broth containing cubes of egg-white; or use serum medium or 

 other sugar-free media; or a medium made up at pH 8.0 or above. 

 For an organism whose morphology interests one and whose nature 

 is not known, experiments should be tried with various media, 

 and the behavior of the mixture should be studied. Under labora- 

 tory conditions certain types always tend to disappear from mixed 

 cultures. It must be kept in mind that conditions must exist in 

 nature which favor the multiplication of such species or they 

 would have died out long ago. For such organisms try media of 

 vegetable origin. 



In taking samples of pathological material enrichment with the 

 tissue in which the organisms are found is advisable. Schott- 

 miiller isolated septicemic streptococci in blood-glucose agar 

 shakes. The many tissue-containing media favor the growth of 

 pathogens. (Media summarized by Pfuhl.) Tunnicliffe used 

 serum and ascites agar for the anaerobic coccus found by her in 

 measles cases. Plotz and his co-workers added ascites or hydro- 

 cele fluid to glucose agar for blood cultures from their typhus 

 patients. Dick and Henry employed blood-glucose agar for 

 the various anaerobes found in the blood of scarlet fever 

 patients. Leucowicz used serum-sugar agar for Fusiformis. 



Digest media are excellent for anaerobes. A number of such 

 media are discussed by Stickel and Meyer. 



Serious problems sometimes arise. Thus, B. tetani is particu- 

 larly difficult to isolate from gross mixtures, as it is not a tissue 

 invader, and because it sporulates later than the organisms that 

 usually accompany it. In case an organism like B. tetani grows 



