98 LABORATORY GUIDE IN BACTERIOLOGY 



2. Label each tube with the name of the culture 

 inoculated, and the date of inoculation. 



3. Place one culture of each organism in the thermo- 

 stat, one culture of B. prodigiosus and B. violaceus in 

 the locker, and leave the others exposed to sunlight. 



4. After 24 hours compare the growths of B. 

 prodigiosus and B. violaceus, under the various condi- 

 tions, in respect to — 



a) Relative amount of growth. 



b) Relative amount of pigment produced. 



5. Note the characteristics of the pigments: Are 

 they diffused through the medium, or are they con- 

 fined to the growth ? 



6. Make descriptions of agar cultures; also hanging- 

 drop, stained, and Gram preparations. 



7. Transfer from 24-hour-old agar cultures of all 

 organisms to all media. (See Section 8.) Potatoes 

 may be inoculated with the looped needle, as the sur- 

 face is too rough to allow of a smooth inoculation with 

 the straight needle. 



8. After all cultures have been incubated for 24 

 hours, make all descriptions as outlined on pp. 53 ff. 



Caution. — Through oversight gelatin cultures are sometimes 

 placed by students in the thermostat. This defeats the purpose 

 of obtaining a stab growth, as the gelatin will melt. In order 

 to avoid this mistake, it is recommended to label one tin cup or 

 tumbler "Gelatin" in large letters. This will serve as a constant 

 reminder that gelatin has to be kept at room temperature. 



9. Make plate cultures of the four organisms. 

 Method of making plates — 



1. Melt two agar tubes for each organism in the 

 water bath and cool to 43° C. 



