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 sterilized by dry heat at about 150° C. for one 
hour, and stored for future use. Thcse 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” 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. 
