8O MANUAL OF BACTERIOLOGY. 



or of 75 G. on each of four days if the serum is to be solidi- 

 fied. In the latter case the tubes are to be placed in an in- 

 clined position. ( See page 67. ) Opaque, coagulated blood- 

 serum has most of the advantages of the clear medium. 

 Blood-serum may be secured from small animals by collect- 

 ing 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, some- 

 times from serous pleural transudates or from hydrocele 

 fluid. The preservation of blood-serum is sometimes accom- 

 plished 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, solidified and 

 sterilized as required ; the chloroform will be driven off 

 by the heat, owing to its volatility. Blood-serum media 

 which are sterilized at low temperatures should be tested for 

 twenty-four hours in the incubator to prove that steriliza- 

 tion 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. 



Lbffler's blood-serum consists of one part of bouillon 

 containing 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 diph- 

 theria. 



Blood-scntm-agar is a medium made with considerable 

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

 ococcus. One part of placental blood-serum, or pleuritic 

 serum, or hydrocele fluid, is mixed with one to two parts 

 of nutrient agar in the fluid condition. It must be divided 

 into tubes before solidification. Solidify in a slanting posi- 



