66 METHODS OF CULTIVATION OF BACTERIA. 



prevent back flow of the fluid, press downwards so as to buckle 

 up the tubing at B and C (Fig. 31). This forms both a water 

 and air tight compartment in A, and readily allows anaerobic 

 growth. 



When it is desired to grow anaerobes on the surface of a 

 solid medium such as agar, tubes of the form shown in Fig. 32, 



a and b, may be 

 use d- A stroke 

 culture having 

 been made, the 

 air is replaced by 

 hydrogen as just 



FIG. 32. Tubes for anaerobic cultures on the surface of solid described, and 



media - the tubes are 



fused at the constrictions. Such a method is of great value 

 when it is required to get the bacteria free from admixture of 

 medium, as in the case of staining flagella. By the use of 

 Novy's jar anaerobes may be made to grow on all media in 

 ordinary culture tubes. 



MISCELLANEOUS METHODS. 



Collodion, or Celloidin Sacs. These were introduced by 

 Metschnikoff, Roux, and Salimbeni during their studies on the 

 spirillum of Asiatic cholera, and further exploited by Nocard 

 and Roux in their research upon the cause of pleuro-pneumonia 

 of cattle. The usefulness of such a sac lies in the fact that liv- 

 ing cultures can be introduced into the body of an animal with- 

 out coming into direct contact with its tissues or body fluids, 

 whilst their soluble products can, through the osmotic proper- 

 ties of the collodion, pass outwards and be absorbed by the tis- 

 sues, and at the same time the animal fluids can pass within and 

 nourish the bacteria. Thus a ready means is afforded of exalt- 

 ing virulence of bacteria, of producing agglutinative and other 

 phenomena, without great difficulties being thrown in the way, 

 such as otherwise might happen. The method used by the French 

 investigators in making the sacs, as stated by Novy, is rather 

 an involved and laborious proceeding, and lately a newer and 

 easier method has been recommended by McCrae, wherein gela- 

 tin capsules are coate^l with collodion and the resulting sac is 

 mounted on glass tubing and prepared for final use. McCrae's 



