68 MANUAL OF BACTERIOLOGY. 



hot-air sterilizer at a temperature below the boiling-point. 

 After coagulation, sterilize as usual. This serum makes an opaque 

 medium of a cream color. Blood-serum may be sterilized in 

 the special form of sterilizer devised for it. A clear blood- 

 serum is to be obtained by sterilization at a temperature of 

 58° C. for one hour, on each of six days, if a fluid medium is 

 desired, or of 75° C. on each of four days if the serum is to be 

 solidified. In the latter case the tubes are to be' placed in an 

 inclined position. (See page 55.) Opaque, coagulated blood- 

 serum has most of the advantages of the clear medium. Blood- 

 serum may be secured from small animals by collecting blood 

 directly from the vessels, using very great care to obtain the 

 blood in a sterile condition; and the serum may be separated 

 and stored in a fluid state. Human blood-serum is sometimes 

 obtained from the placental blood, sometimes from serous 

 pleural transudates or from hydrocele fluid. The preservation 

 of blood-serum is sometimes accompHshed with chloroform, of 

 which I per cent, is to be added to the medium; in this manner 

 the serum may be preserved for a long time. It may be divided 

 into tubes, soHdified and sterilized as required; the chloroform 

 is driven off by the heat, owing to its volatility. Blood- 

 serum media which are sterihzed at low temperatures should 

 be tested for twenty-four hours in the incubator to prove that 

 sterilization has been effective; if it has not, development of 

 the contaminating bacteria will take place and be visible to the 

 eye. 



It will be impossible to do more than merely mention some 

 of the most important of the other culture-media. 



Loffler's blood-serum consists of one part of bouillon con- 

 taining I per cent, of glucose, and three parts of blood-serum. 

 It is sterilized like ordinary blood-serum. It is used largely for 

 the cultivation of the bacillus of diphtheria. 



Blood-serum-agar is a medium made with considerable 

 difficulty, but very valuable for the cultivation of the gon- 



