212 BIOLOGY AND TECHNIQUE 



Bacteriological examination of feces is most often undertaken 

 for the isolation of Bacillus typhosus, dysentery, cholera, etc. These 

 methods are discussed in detail in the chapters dealing with the 

 diseases. See also section on media. 



The determination of tubercle bacilli in stools is difficult and of 

 questionable significance, in that they may be present in people 

 suffering from pulmonary tuberculosis as a consequence of swallow- 

 ing sputum or infected food, and in that there may be other acid- 

 bacilli, such as the timothy bacillus, present. Perhaps the most 

 reliable method is to treat a suspension of the feces with 5 per cent 

 antiformin over night, centrifugalize thoroughly, wash the sediment, 

 and inject into guinea pigs. 



Blood Cultures. The diagnosis of septicemia can be positively 

 made during life only by the isolation of bacteria from the blood. 

 Such examinations are of much value and are usually successful 

 if the technique is properly carried out. A large number of methods 

 are recommended, the writers giving, however, only the one which 

 they have found successful and simple for general use. 



The blood is taken by preference from the median basilic vein 

 of the arm. If, for some reason (both forearms having been used 

 for saline infusion), these veins are unavailable, blood may be taken 

 from the internal saphenous vein as it turns over the internal 

 malleolus of the ankle joint. The skin over the vein should be 

 prepared before the specimen is taken by painting with iodin, as 

 for a surgical operation. The syringe which is used should be of 

 some sterilizable variety (the most convenient the Luer model), 

 which is easily manipulated and does not draw with a jerky, irregular 

 motion. Its capacity should be at Jeast 10 c.c. It may be sterilized 

 by boiling for half an hour, or preferably, when all-glass syringes 

 are used, they may be inserted into potato-tubes and sterilized at 

 high temperature in the hot-air chamber. Before drawing the blood, 

 a linen bandage is wound tightly about the upper arm of the patient 

 in order to cause the veins to stand out prominently. When the 

 veins are plainly in view, the needle is plunged through the skin 

 into the vein in a direction parallel to the vessel and in the direction 

 of the blood-stream. After perforation of the skin, while the needle 

 is groping for the vein, gentle suction may be exerted with the 

 piston. Great care should be exercised, however, that the piston 

 is not allowed to slip back, and air be, by accident, forced into the 

 vessel. In most cases no suction is necessary, the pressure of the 





