METHODS OF CULTURE AND OF EXAMINATION. 77 



struction is rather expensive. Disinfection under increased 

 pressure has the great advantage that it is effected much 

 more rapidly; with a temperature of 120 C. (248 F.), 

 about fifteen or twenty minutes are required to destroy all 

 germs, even the especially resistant spores of some bacilli of 

 food and of earth which are not destroyed with certainty by 

 free steam even after an exposure of five hours. The objection 

 has been raised to disinfection with steam under pressure 

 that it does not sterilize with certainty because a tempera- 

 ture of 120 C. (248 F.) does not prevail in all parts of the 

 autoclave. This objection is, however, not justifiable. It 

 is only necessary to be certain that no trace of air is left 

 in the apparatus, and to this end the valve is closed after 

 generation of steam has been taking place for five minutes. 

 The sterilization of certain fluids containing albuminoid 

 substances requires special precautions. Live, or even 

 compressed, steam can not be employed for this purpose, 

 inasmuch as coagulation would take place. Resort must, 

 therefore, be had to so-called fractional, or discontinuous, 

 sterilization (Tyndall). The fluids to be disinfected are ex- 

 posed for four or five hours to a constant temperature of 

 from 56 C. (132.8 F.) to 58 C. (136.4 F.). Exposure 

 for four hours to a temperature of 58 C. (136.4 F.) is 

 sufficient to destroy most developed bacteria. The spores 

 that remain in consequence of their greater resistance are 

 now permitted to germinate, by leaving the fluid undisturbed 

 for twenty-four hours. After the lapse of this interval, the 

 fluid is again exposed for four hours to a temperature of 

 from 56 C. (132.8 F.) to 58 C. (136.4 F.) ; and this 

 mode of procedure is repeated daily for a whole week. At 

 the end of this time all of the spores will have developed 

 into bacteria, and these will in turn have been destroyed. 

 This method is not, however, trustworthy under all condi- 

 tions, as spores may develop after the lapse of a week. It 

 appears better to introduce the albuminoid fluids (blood- 

 serum, etc.) in small amounts into test-tubes or the like 

 (Fig. 1 2), and to expose these for a considerable length of 

 time (from four to six hours) to a temperature of from 

 56 C. (132.8 F.) to 58 C. (136.4 F.), and then to place 

 them for two days in the thermostat at a temperature of 

 37 C. (98.6 F.). The tubes in which contaminations 

 appear are set aside. With care in manipulation the number 

 of turbid tubes will rarely be large. Fractional sterilization 



