226 BACTERIOLOGICAL EXAMINATION OF MATERIAL 



three minutes. Then the point of the needle is gently inserted into 

 the vein (which may be made prominent by gentle pressure with a 

 tourniquet applied to the arm above the elbow), and from 5 to 20 c.c. 

 of blood withdrawn. This is introduced at once into broth, as outlined 

 above. 1 



It may be desirable to estimate the number of bacteria in the blood : 

 1 c.c. of blood is mixed at once with 10 c.c. of agar previously melted 

 and cooled to 42 C., and plated in a Petri dish. If desired, dilution 

 may be made 1 to 10, 1 to 100 in succeeding tubes of agar. 



Typhoid and paratyphoid bacilli grow readily in the broth cultures. 

 They may be identified by their cultural and agglutination reactions 

 with highly potent specific sera. Streptococcus and pneumococcus 

 cultures are obtained in a similar manner from the blood stream in 

 blood bouillon. The organisms are isolated in pure culture by smear- 

 ing the broth, after incubation, upon the surface of freshly prepared 

 blood agar plates. The Streptococcus colonies usually exhibit a wide 

 clear zone of hemolysis. Pneumococcus colonies are characterized by 

 a narrower green zone of altered blood pigment around them. Plague 

 bacilli and Micrococcus melitensis are frequently detected in the 

 blood stream; occasionally the organisms are present in sufficient 

 numbers to develop in blood agar plates inoculated with 1 to 2 c.c. 

 of blood. The former produces characteristic lesions in guinea-pigs; 

 the latter develops very slowly, frequently becoming visible only after 

 five to seven days' incubation. 



Bacteriological Examination of Cerebrospinal Fluid. Spinal fluid 

 for bacteriological examination is obtained by lumbar puncture with 

 a sterile hypodermic needle, or fine trochar about 8 cm. long and 1 

 mm. in bore. The needle is introduced preferably in the fourth intra- 

 vertebral space; the fasciculi of the cauda equinum are not tense at 

 this level and are readily pushed aside by the needle without injury. 

 An imaginary line touching the crests of the ilia intersects the spinous 

 process of the fourth lumbar vertebra; the sterile needle is inserted 

 through the previously sterilized skin at a point 1 cm. to the right 

 (or left) of the lower rim of the spinous process, and directed obliquely 

 upward and inward to such a degree that the point of the needle will 

 reach the median line at a depth of 5 to 6 cm. The subarachnoid space 

 is reached at this level and resistance to the passage of the needle 



1 Occasionally circumstances arise which make it necessary to send the blood to a 

 distance for examination; mixing the blood with an equal volume of glycerine bile (one 

 part glycerin, ten parts ox bile; sterilize in autoclave) is said to be an efficient method 

 for preserving the bacterial content of blood practically unchanged for several hours. 



