PREPARATION OF CULTURE MEDIA 37 



a finger and then wash with alcohol, allow the alcohol to evaporate 

 and then with a sterile needle prick the finger. Take up a drop 

 of the blood with a sterile platinum loop and smear it on the sur- 

 face of an agar slant. Agar poured out in a thin layer in a Petri 

 dish may be smeared with blood in the same way and used for 

 cultures. It is advisable to incubate the blood-smeared medium 

 for 24 hours before inoculating to be sure that it is sterile. 



Organisms such as the gonococcus, pneumococcus, and influ- 

 enza bacillus, which do not grow readily on ordinary agar, are culti- 

 vated on this medium. 



14. Hiss Serum Water. Beef serum is drawn in a pipette 

 from clotted blood and added to distilled water in the proportion 

 of one part of serum to two or three parts of w r ater. The mixture 

 is heated in the Arnold for 15 minutes at 100 C. to destroy any 

 sugar fermenting enzyme present in the serum, after which sufficient 

 aqueous solution of litmus is added to give a transparent blue color. 

 One per cent of the desired sugar (glucose, saccharose, lactose, etc.) 

 is added and the medium is tubed and sterilized by the fractional 

 method in the Arnold. 



This medium is of use in determining the ability of a species to 

 ferment different carbohydrates and also its power to coagulate 

 serum protein. 



Method of Obtaining Serum. Beef or sheep's blood is collected 

 in a sterile jar at the slaughter house. After coagulation the 

 clot should be carefully separated from the sides of the container 

 with a sterile glass rod and the jar placed in the refrigerator for 

 24 hours. At the end of this time the clear serum can be pipetted 

 or siphoned off with sterile glass tubing and placed in sterile flasks. 

 Serum may be sterilized in its fluid state by exposure to a temper- 

 ature of 60 C. for one hour upon six consecutive days. 



Exudates from the pleural or abdominal cavity may be used 

 instead of beef or sheep serum. The fluid is allowed to flow directly 

 out of the canula into sterile flasks. The instruments should be 

 taken into the ward in sterile water and not in an antiseptic solu- 

 tion. Before using the fluid should be incubated and any flasks 

 showing contamination should be discarded. 



