BACTERIOLOGICAL EXAMINATIONS 109 



the sodium citrate. Five c.c. of blood is added to a flask con- 

 taining 100 c.c. of glucose meat infusion broth, 1 c.c. to each of 

 two or three test tubes of broth, and 1 c.c. to two or three tubes 

 of glucose agar, cooled to 40 C. The latter are thoroughly mixed 

 by a rotary motion to avoid the formation of air bubbles, after 

 which the necks of the tubes are flamed and the contents carefully 

 poured into Petri dishes. This procedure not only makes possible 

 the isolation of the organisms, it also enables a rough estimate to 

 be made of the number present. From the broth tubes other 

 tests may be made if the organism is obtained in pure culture. 



Solid Organs. When solid organs are to be examined about 

 one inch of the surface is seared with a hot spatula or scalpel in 

 order to kill all extraneous organisms. An incision is made in 

 the seared area with a sterile scalpel and small quantities of the 

 fluid within the organ removed with a platinum loop and trans- 

 ferred to suitable media. 



Examination of Bacteria in Tissues. In order to examine 

 bacteria in body tissues the latter must be fixed, hardened, and 

 cut in extremely thin section. 



Fixation consists in treating the tissue in such a manner that it 

 will preserve as far as possible its condition at the time of removal 

 from the body ; hardening renders it firm enough to be cut in very 

 thin sections with a microtome. 



The best results are obtained by embedding in solid paraffin. 

 Impregnation with paraffin in the melted state gives, when solidi- 

 fied, support to the tissue elements and greatly facilitates the 

 cutting process. After hardening, the tissue is dehydrated and 

 then completely permeated by a solvent of paraffin which will 

 rid the tissue of the dehydrating fluid and at the same time make 

 possible the entrance of the paraffin. The solvents in general use 

 are chloroform, cedar oil, xylol, and turpentine. 



Several methods of more or less value have been devised. The 

 following is simple and gives good results. 



Fixation. As soon as possible after removal from the body 

 small pieces of tissue about -j- inch by i inch are cut and placed 

 in the fixative prepared as follows: To a heated 0.75 per cent 



