310 BACTERIOLOGY. 



A better and more useful procedure than the above is 

 to employ gelatin containing two per cent, of glucose and 

 colored with litmus. The ordinary test-tubes containing 

 this material are inoculated and placed direct in the incuba- 

 tor at 37°. 



Although the gelatin melts and apparently there is 

 free access of air, yet abundant growths of all the anae- 

 robic bacteria can thus be obtained. Similar, though not 

 as constant results have been obtained with glucose bouil- 

 lon containing two per cent, of gelatin. The viscosity of 

 the liquid undoubtedly prevents the penetration of the air. 

 The cultures grown in litmus colored glucose gelatin pre- 

 serve their vitality better than on any other medium. 

 Moreover, they possess another advantage in this that the 

 growth is readily accessible for transplantation or for 

 study. For these reasons it is the author's usual method 

 for keeping stock cultures of anaerobes. 



Microbic association. — The soil seems to be the natural 

 habitat of the anaerobic bacteria. And yet, of all places 

 this would seem to be the least adapted for their growth 

 owing to the abundance of oxygen. When a strongly 

 aerobic organism, such as the B. prodigiosus or Proteus 

 vulgaris, is inoculated into a tube of bouillon, and, if at the 

 same time an anaerobic organism is planted, it will be 

 found that both bacteria will develop. Apparently the 

 aerobic form consumes the oxygen in the immediate neigh- 

 borhood of the anaerobic organism, and thus allows the 

 latter to develop. Such cultures are intensely virulent. 

 Conditions of this kind not only favor the growth of anae- 

 robic bacteria in the soil, but are known to bring on dis- 

 ease. Tetanus or lock-jaw is induced in this way, as a 

 result of such microbic associations. 



Of the several methods touched upon in the preceding 

 summary two deserve especial attention owing to their 

 practical usefulness. In these the ordinary test-tubes are 



