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.' 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. 

 Tbis insures neutrality, permitting pneumococci or streptococci, which 

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



In making blood cultures from typhoid patients, various methods 

 have been recommended. Buxton and Coleman ^ have obtained excel- 

 lent results by the use of pure ox-bile containing 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 in order to insure high dilution. 



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

 nation usually offers little difficulty. If the same microorganism ap- 

 pears in several of the plates and flasks, if colonies upon the plates are 

 well disxributed 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 sapro- 

 phytic upon the skin or in the air, they must be looked upon with ex- 

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

 cultures skeptically, discarding Staphylococcus albus as a contamina- 

 tion, and taking, if possible, another corroborative culture when the 

 organism is Staphylococcus pyogenes aureus. 



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



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



