DIPHTHERIA BACILLUS. 379 



(Fig. 22) or a double boiler serves best, though a steam 

 sterilizer will suffice. If the latter is used a wire 

 frame must be arranged to hold the tubes at the proper 

 inclination, and the degree of heat must be carefully 

 watched, as otherwise the temperature may go too 

 high, and if the serum is actually boiled the culture 

 medium will be spoiled. After sterilization by this 

 process the tubes containing the sterile, solidified blood- 

 serum can be placed in covered tin boxes or stopped 

 with sterile corks and kept for months. The serum thus 

 prepared is quite opaque and firm. A mixture of blood- 

 cells renders the serum darker, but it is not less useful. 



The Swab for Inoculating Culture Tubes. The swab 

 to inoculate the serum is made as follows : A stiff, thin 

 iron rod, six inches in length, is roughened at one end 

 by a few blows of a hammer, and about this end a little 

 absorbent cotton is firmly wound. Each swab is then 

 placed in a separate glass tube, and the mouths of the 

 tubes are plugged with cotton. The tubes and rods are 

 then sterilizt d by dry heat at about 150 C. for one 

 hour, and stored for future use. Th<se cotton swabs 

 have proved much more serviceable for making inocu- 

 lations than platinum wire needles, especially in young 

 children and in laryngeal cases. It is easier to use the 

 cotton swab in such cases, and it gathers up so much 

 more material for the inoculation that it has seemed 

 more reliable. 



For convenience and safety in transportation a " cul- 

 ture outfit' 7 has been devised, which consists of a small 

 wooden box containing a tube of blood-serum, a tube 

 holding a swab, and a record blank. These " culture 

 outfits " may be carried or sent by messenger or ex- 

 press to any place desired. 



