180 BIOLOGY AND TECHNIQUE 



cooled to 41 in order that bacteria, if present, may not be injured by 

 the heat. The blood is added to the tubes in varying quantities, ranging 

 from 0.25 to 1 c.c. each, in order that different degrees of concentration 

 may be obtained. Mixing is accomplished by the usual dipping and 

 rotary motion, the formation of air-bubbles being thus avoided. The 

 mouth of each test tube should be passed through the flame before pour- 

 ing the contents into the plates. Three flasks of glucose broth, contain- 

 ing 100 to 150 c.c. of fluid each, should be inoculated with varying 

 quantities of blood at least one of the flasks containing the blood in 

 high dilution. The most stringent care in the withdrawal and replace- 

 ment of the cotton stoppers should be exercised. 1 The writers have 

 found it convenient to use, in place of one of these flasks, one containing, 

 in addition to the glucose, 1 gm. of powdered calcium carbonate. 

 This insures neutrality, permitting pneumococci or streptococci, which 

 are sensitive to acid, to develop and retain their vitality. 



In making blood cultures from typhoid patients, Buxton and Cole- 

 man 2 have obtained excellent results by the use of pure ox-bile con- 

 taining ten per cent of glycerin and two per cent of peptone in flasks. 

 The writers have had no difficulty in obtaining typhoid cultures by the 

 use of slightly acid meat-extract broth in flasks containing 200 or more 

 c.c. to which comparatively little blood has been transferred. 



ANAEROBIC BLOOD CULTURES. These cultures may be taken by 

 mixing blood in deep tubes with glueose-ascitic agar, covering with 

 albolene and putting into Novy jars. 



In estimating the results of a blood culture, the exclusion of con- 

 tamination usually offers little difficulty. If the same microorganism 

 appears in several of the plates and flasks, if colonies upon the plates 

 are well distributed within the center and under the surface of the 

 medium, and if the microorganisms themselves belong to species which 

 commonly cause septicemia, such as streptococcus and pneumococcus, 

 it is usually safe to assume that they have emanated from the patient 's 

 circulation. When colonies are present in one plate or in one flask 

 only, when they are situated only near the edges of a plate or upon 

 the surface of the medium, and when they belong to varieties which 

 are often found saprophytic upon skin or in air, they must be looked 

 upon with suspicion. It is a good rule to look upon all staphylococcus 

 albus cultures skeptically. 



1 Small Florence flasks are preferable to the Erlenmeyer flasks usually employed. 



2 Buxton and Coleman, Am. Jour, of Med. Sci., 1907. 



