BACTERIOLOGICAL lECHNIC 



71 



sterile jar or flask, closed with cotton plug. Place on ice for twenty-fqur 



to forty-eight hours, during which time coagulation has taken place; the 



serum may then be siphoned off. The proper sterilization of Loeffler's 



serum requires care. After the bouillon and serum 



are mixed, pour into test-tubes and coagulate in a 



Koch serum coagulator at a temperature of 80° C. 



Any form of sterilizer may, however, be used. The 



essentials are that the temperature should be raised 



very gradually and must be kept below the boiUng- 



point, and the tubes should be slanted at a degree 



which will bring the medium close to the cotton plug, 



making what are commonly called tube slants. After 



the medium is coagulated in the -tubes it is sterihzed 



fractionally on three successive days (one hour each 



day) at a temperature of 80° C. These tube slants 



are now ready for the physician. 



To prevent evaporation of the medium in the 

 test-tubes, cover the cotton plug and upper end of 

 tube with tin foil fastened with thread, and dip into 

 melted paraffin several times. Tubes thus sealed can 

 be kept for a year or more without any considerable 

 shrinking of the medium. Dip the tin foil in a i : 2000 

 corrosive sublimate solution before capping on tubes. 



A simpler way is to use rubber caps which are 

 especially made to fit over the end of the test-tube 

 and the cotton plug. These rubber caps must be 

 sterilized before applying them, for which purpose 

 the 1-2000 corrosive sublimate solution will be found satisfactory. 

 Rubber stoppers may also be used but they are more expensive and 

 inferior to the rubber cap or the tin foil with coat of paraffin. 



C. Liquid Blood Serum. — ^Obtained as for Loeffler's serum. Sterilize 

 fractionally at a temperature of from 56° to 58° C. for one hour on each 

 of six days. The serum will be liquid and clear. 



D. Milk. — Secure fresh milk directly from cow, or, if in cities, demand 

 certified milk. Keep on ice, in a covered jar, for twenty-four hours. 

 Siphon off the middle portion, rejecting cream and sediment. Sterilize 

 like Loeffler's blood serum. Litmus milk is prepared by adding i per cent, 

 of azohtmin before sterilizing. This indicator will show whether or not 

 acids are formed by the microbes which may be cultivated in the milk. 

 Only pure milk will answer the purpose. Milk to which preservatives 

 (formaldehyd, salicylic acid, borax, boric acid) have been added must 

 not be used. 



Fig. 19. — Cul- 

 ture tube and swab 

 tube used by phy- 

 sicians in the diag- 

 nosis of diphtheria. 

 The swab tube 

 should be long 

 enough to have the 

 entire length of swab 

 inside, not project- 

 ing as shown in the 

 figure. (Williams.) 



