BLOOD MEDIA 45 



The excess of the blood runs down and leaves a film on the 

 surface. Cover the tubes with indiarubber caps, and incubate 

 them for one or two days at 37° C. before use, to make certain 

 that they are sterile. Agar poured out in a thin layer in a 

 Petri dish may be smeared with blood in the same way and 

 used for cultures. 



Serum-Smeared Agar is prepared in a similar way by smear- 

 ing the surface of the agar with blood serum, or by adding a few 

 drops of serum to the tube and then allowing it to flow over the 

 surface. 



Blood Agar. — For many purposes (e.g., the growth of the 

 whooping-cough bacillus, the bacillus of soft sore, the cultivation 

 of trypanosomes and Leishmaniee), the use of agar containing 

 defibrinated blood, especially rabbit blood, is desirable. The 

 blood may be obtained in several ways, preferably by bleeding 

 from the carotid. For this purpose the vessel is exposed and 

 as long a portion as possible is cleaned. This is ligatured high 

 up, and a ligature is loosely applied round the lower part of 

 the vessel in such a way as not to constrict it. The vessel is 

 clamped above this ligature, and with scissors an oblique 

 opening is made in its side. The clamp being removed, the 

 stream of blood is directed by means of the ligature into the 

 mouth of a stout sterile flask, which ought to contain some 

 fragments of broken glass rod. During the bleeding the flask 

 should be gently agitated, and when filled should be shaken in 

 a bath of water just below blood-heat. We have found that 

 sterile blood can be obtained from the ear vein of the rabbit by 

 the method of bleeding to be subsequently described (p. 126). 

 The ear is well washed with lysol, the lysol dried off with sterile 

 wool, absolute alcohol dropped on and allowed to evaporate, 

 and the blood withdrawn. The first c.c. or so is rejected. 



However the blood is obtained, after defibrination it is warmed 

 to 45° O, and added to agar of the same temperature in the 

 proportion of about one-third of blood and two-thirds of agar. 

 Needless to say, such media must be incubated before use to 

 ensure that bacteria have not gained access during preparation. 



Bordet and Gengou'a Medium for Bacillus of Whooping-Cough. — 



An extract of potato is first prepared by adding two parts of water con- 

 taining 4 per cent, of glycerin to one part of potato chips ; the mixture 

 is then boiled and the fluid is separated off. An agar medium is then 

 prepared of the following composition : potato ex'tract, 50 c.c. ; '6 percent, 

 solution of sodium chloride, 150 c.c. ; and agar, 5 grms. Of this medium, 

 2-3 e.c. are placed in each of a series of sterile test-tubes, and then to each 

 there is added, by the method described in the preceding paragraph, an 

 equal part of defibrinated rabbit's (or better, human) blood, obtained 



