46 MEDICAL BACTERIOLOGY 



Add 10 per cent, (by weight) of sterile distilled water. Mix. Filter through 

 gauze, tube, slant and sterilize in steam sterilizer at 7oC. for 2^ hours. 



In emptying eggs from shell care must be taken to prevent the eggs from 

 contact with the outside of the shell or fingers; when mixing with water and tub- 

 ing, bubbling must be avoided. 



Potato Medium. Take a smooth, new potato, wash in water (hot), hot i : 500 

 bichloride; then, in several changes of hot water. Cut cylindrical pieces about 

 i^ inches long and about the same diameter as the tubes in which they are 

 to be placed. Split each cylinder diagonally in two through long axis, place 

 each piece in a tube with the thick end at the bottom and add about }/ inch of 

 distilled water. 



Sterilize in autoclave. 



Petroff's Medium. 



2 parts egg (whites and yolks). 



i part meat juice.- 



Gentian violet in i : 10,000 dilution. 



Meat juice infuse 500 Gm. of veal in 500 cc. of 15 per cent. sol. glycerin 

 in H2O for 24 hours and strain off juice. 



Eggs sterilize shells with 20 per cent, carbolic acid and break into sterile 

 beaker and mix well. Then filter through gauze, adding i part of the infusion 

 by volume. 



Gentian violet add sufficient i per cent, alcoholic gentian violet to make a 

 dilution of i : 10,000. 



Tube and sterilize in steam sterilizer or inspissate for 3 successive days, 

 8oC. for i hour each day. 



Modification of Petroff's Medium. (By Williams-Burdick). 



1. Egg-white Solution. This is made by diluting the egg white with 

 10 parts of distilled water and thoroughly shaking. The fluid is opalescent 

 and contains numerous whitish flakes. To clear it, pass it through a thin layer 

 of cotton and then heat to iooC. to hasten precipitation. It is then filtered 

 through paper. 



2. Egg-yolk Solution. The yolks are diluted with 10 parts of water and 

 well stirred. The cloudy emulsion is clarified by adding normal sodium hydrox- 

 ide. Too much hydroxide is harmful and therefore complete solution of the 

 yolk is not desirable. The emulsion should be slightly turbid. To attain the 

 proper degree of turbidity, i cc. of normal NaOH is usually added to each 100 

 cc. of emulsion. This is not a constant amount, however, because some yolks 

 will be completely dissolved by less than half this amount of alkali. The solu- 

 tion is heated to iooC. and filtered. 



3. Meat Infusion. 500 Gm. of finely chopped lean veal are covered with i 

 liter of water containing 15 per cent, glycerin, allowed to infuse for 24 hours and 

 filtered; 5 Gm. NaCl are added and the infusion heated to boiling. It is again 



