114 



BACTERIOLOGY. 



plugged sterilised test-tubes. These should be filled, with a sterilised 

 pipette, to about one-third of their capacity. 



Formerly the tubes were sterilised by Tyndall's process of dis- 

 continuous sterilisation. The tubes were placed in Koch's serum 

 steriliser, with the temperature maintained for an hour or more at 

 56 C., and this was repeated for six successive days, the temperature 

 on the last day being gradually raised to 60 C. This completed the 

 sterilisation, and to solidify the serum the tubes were arranged in 

 the inspissator at the angle required, and the temperature was kept 



between 65 C. and 68 C. 

 Directly solidification took 

 place the tubes were removed. 

 The new process is much 

 less tedious, and consists in 

 taking every possible pre- 

 caution to obtain the blood 

 without contamination by bac- 

 teria in the air or in the 

 vessels employed. There is 

 then no need to sterilise the 

 serum, and it can be coagu- 

 lated immediately. The tubes 

 are tested by placing them 

 in an incubator at 37 C. for 

 a week, and if any show 

 signs of contamination they 

 are discarded, and the rest 

 can be used or kept in stock. 



The serum should then 



present the character of being hard, solid, of a pale straw colour, 

 and transparent. A little liquid collects at the lowest point, and 

 the serum is sometimes milky in appearance at -its thickest part. 



Loffler's Blood Serum is prepared by mixing two- thirds of fresh 

 serum with one-third of broth, prepared in the usual way but with 

 the addition of 1 per cent, grape-sugar. The mixture is decanted 

 into test-tubes, avoiding the formation of air- bubbles, and it is then 

 coagulated in the usual way. The serum may be employed not only 

 in test-tubes, but also in small flasks, glass capsules, or other vessels, 

 all of which must be cleansed and sterilised. 



Hydrocele fluid and other serous effusions may be prepared in 

 the same manner. (Gelatine may be added to the serum in the pro-- 

 portion of 5 per cent. 



FIG. 43. KOCH'S SERUM STERILISER. 



