INOCULATION OF GELATINE AND AGAR. 61 



the material and the growth occurs, or the medium is punctured 

 with a stab of the platinum rod containing the material. The 

 first is called a stroke or smear culture, the second a stab or thrust 

 culture. In removing the cotton plugs from the sterile tubes to 

 carry out the inoculation, the plugs should remain between the 

 fingers in such a way that the part which comes in contact with 

 the mouth of the tube will not touch anything. 



After the needle has been withdrawn the plugs are re-inserted 

 and the tubes labelled with the kind and date of culture. 



Plate Cultures. Several tubes of the culture medium are 

 made liquid by heating in water bath, and then inoculated with 

 the material as follows . A looped platinum needle is dipped 

 into the material and then shaken in the tube of liquid media, 

 (gelatine, agar, etc.). 



This first tube is called original. From this three drops (taken 

 with the looped platinum rod) are placed in a second tube, the 

 rod being shaken somewhat in the gelatine or agar ; this is 

 labeled first dilution (a colored pencil is useful for such markings). 

 From the first dilution three drops are taken into a third tube, 

 which becomes the second dilution. (Fig. 29.) 



The plugs of cotton must be replaced after each inoculation, 

 and during the same must be carefully protected from contami- 

 nation. 



To hasten the procedure and lessen the danger of contamina- 

 tion, the tubes can be held in one hand aside of each other, each 



FIG. 30. 



Manner of holding plugs. 



plug opposite its tube. They are now ready for spreading on 

 glass plates. 



