and Laboratory Methods. 



1801 



gelatin, the inoculated medium is almost entirely protected from the 

 access of the atmosphere. 



Schill's modification of the above method : Pour from 10 to 15 c. c. 

 of liquified gelatin or agar into a large test tube, inoculate it with the 

 anaerobic organism, insert a narrow sterile test tube into the inoculated 

 medium in the large tube and roll the whole apparatus in ice water or 

 on a cake of ice. When the operation is completed the thin layer of 

 solidified medium in the outer tube is protected from the air by the I ^ 

 inner, smaller test tube. Both methods have the advantage over the 

 ordinary Esmarch roll culture that they furnish a support for the thin 

 layer of culture medium, and prevent it from sliding down to the bottom fig. 37. 

 of the tube. 



B. LAYER OF OIL. 



This method, illustrated in Fig. 37, and used by Pasteur and Hesse, offers to 

 be of little if any advantage over those described under A. 



Method. — Pour about 7 c. c. (in case of small tube) and 15 c. c. (in case of 

 large tube) of liquified gelatin or agar into a sterile test tube, boil 

 to expel the air, cool to 40°C., inoculate without shaking the tube, 

 cool rapidly in ice water until the medium is set and pour a layer 

 of sterile oil on the surface of the inoculated medium. This 

 method may also be used for stab cultures (see Fig. 38). Cultures 

 prepared in this way have the disadvantage that the oil which ad- 

 heres everywhere renders them somewhat objectionable. 



Fig. 38. 



C. LAYER OF PARAFFIN. 



Kitasato was the first to use paraffin as a cover over the inoc- 

 ulated medium. He poured liquified paraffin on the inoculated 

 medium. This method has several disadvantages ; with the 

 paraffin foreign germs may be introduced into the medium, the 

 neck of the culture apparatus is smeared with the paraffin, and 

 the heat of the liquified paraffin may be injurious or even detri- 

 mental to the development of the inoculated organisms. 



Kasparec (1896) introduced the following method: Use a 

 flask with a long tapering neck as illus- 

 trated in Fig. 39. Blow a small lateral 

 tube, terminating in a bulb, into the neck 

 of the flask, about 1 cm. above (c). Fill 

 the sterile flask with bouillon almost to 

 the neck, then add about 3 c. c. of 

 liquid paraffin and sterilize the whole in 

 the steam sterilizer. The heat expands 

 the bouillon and causes the paraffin to 

 rise in the neck of the flask and to over- 

 flow into the lateral tube, filling the bulb 

 (a), so that after sterilization there re- 

 mains only a very thin layer of paraffin Fig. 39. 



