70 LABORATORY GUIDE IN BACTERIOLOGY 



6. Note the characteristics of the pigments : Are they 

 diffused through the medium, or are they confined to 

 the growth ? 



7. Make descriptions of agar-cultures ; also hanging- 

 drop, stained, and Gram preparations. 



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

 organisms to all media. (See routine study, Chap. IX.) 

 Potatoes may be inoculated with the looped needle, as 

 the surface is too rough to allow of a smooth inoculation 

 with the straight needle. 



9. After all cultures have been in the thermostat for 

 24 hours, make all descriptions as outlined in Chap. X. 

 (Record after 48 hours and 6 days only observations of 

 change.) 



CAUTION. The gelatin-cultures are sometimes placed by 

 students in the thermostat along with others through oversight. 

 This, of course, completely 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. 



10. Make plate-cultures of the four organisms. 

 Method oj making plates 



a) Melt two agar-tubes for each organism in the water- 

 bath and cool to 43. 



b) Transfer 3-5 loopfuls (according to the intensity 

 of the growth, to be judged by the degree of cloudiness) 

 of the broth-culture to a sterile tube of Dunham's solu- 

 tions. (Dilution i). 



c) Shake well, avoiding air-bubbles as much as 

 possible. 



d) Transfer 4 or 5 loopfuls from this suspension to a 

 melted agar-tube, and label this 2. (Dilution 2). 



