FREE BOOKS

Author's List




PREV.   NEXT  
|<   104   105   106   107   108   109   110   111   112   113   114   115   116   117   118   119   120   121   122   123   124   125   126   127   128  
129   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   >>   >|  
ing position in the inspissator at 75 deg. C. for one hour. 9. Place the tubes for forty-eight hours in the incubator at 37 deg. C., and eliminate any contaminated tubes. To prevent drying, 0.5 c.c. glycerine bouillon (see page 209) may be added to each tube between steps 8 and 9. 10. Cap those tubes of media which remain sterile with india-rubber caps and store for future use. ~Potato.~-- 1. Choose fairly large potatoes, wash them well, and scrub the peel with a stiff nail-brush. 2. Peel and take out the eyes. 3. Remove cylinders from the longest diameter of each potato by means of an apple-corer or a large cork-borer (i. e., one of about 1.4 cm. diameter). The reaction of the fresh potato is strongly acid to phenolphthalein. If, therefore, the potatoes are required to approximate +10, as for the cultivation of some of the vibrios, the cylinders should be soaked in a 1 per cent. solution of sodium carbonate for thirty minutes. 4. Cut each cylinder obliquely from end to end, forming two wedge-shaped portions. 5. Place a small piece of sterilised cotton-wool, moistened with sterile water, at the bottom of a sterile test-tube; insert the potato wedge into the tube so that its base rests upon the cotton-wool. Now plug the tube with cotton-wool (Fig. 111). 6. Sterilise in the steamer at 100 deg. C. for twenty minutes on each of _five_ consecutive days. [Illustration: FIG. 111.--Potato tube.] NOTE.--The cork borer reserved for cutting the potato cylinders should be silver electro-plated both inside and out, and the knife used for dividing the cylinders should be of silver or silver plated. When these precautions are adopted the potato wedges will retain their white color and will not show the discoloration so often observed when steel instruments are employed. ~Beer Wort.~--Wort is chiefly used as a medium for the cultivation of yeasts, moulds, etc., both in its fluid form and also when made solid by the addition of gelatine or agar. The wort is prepared as follows: 1. Weigh out 250 grammes crushed malt and place in a 2-litre flask. 2. Add 1000 c.c. distilled water, heated to 70 deg. C., and close the flask with a rubber stopper. 3. Place the flask in a water-bath regulated to 60 deg. C. and allow the maceration to continue for one hour. 4. Strain through butter muslin into a clean flask and heat in the steamer for thirty minutes. 5. Filter th
PREV.   NEXT  
|<   104   105   106   107   108   109   110   111   112   113   114   115   116   117   118   119   120   121   122   123   124   125   126   127   128  
129   130   131   132   133   134   135   136   137   138   139   140   141   142   143   144   145   146   147   148   149   150   151   152   153   >>   >|  



Top keywords:
potato
 

cylinders

 

minutes

 

sterile

 

cotton

 
silver
 
cultivation
 

Potato

 
diameter
 

rubber


potatoes

 

thirty

 
steamer
 

plated

 
reserved
 

retain

 
Sterilise
 
inside
 

electro

 

cutting


consecutive

 

dividing

 

precautions

 

adopted

 

twenty

 

wedges

 

Illustration

 

chiefly

 

heated

 

stopper


distilled

 
crushed
 

regulated

 

muslin

 

Filter

 
butter
 

maceration

 
continue
 

Strain

 
grammes

medium
 

yeasts

 
moulds
 
employed
 

instruments

 

discoloration

 
observed
 

prepared

 
gelatine
 

addition