. Carnegie Institution of Washington publication. PREPARATION OF NUTRIENT AGAR. 35 , r>v '"••/;•' I P {/•• *-»' ^/iv/tt ,'/v?5l ^ii\7C^7IV/" occasional additions of small quantities of water until it is thoroughly cooked in the form of a thick mush. It is then put into the remainder of the water or bouil- lon and subjected to streaming1 steam for two hours, after which, if the first heating was sufficient, it filters readily without the use of a hot-water filter, or the necessity of keeping it in the steamer during the filtering. The stirring rod must touch all parts of the bot
. Carnegie Institution of Washington publication. PREPARATION OF NUTRIENT AGAR. 35 , r>v '"••/;•' I P {/•• *-»' ^/iv/tt ,'/v?5l ^ii\7C^7IV/" occasional additions of small quantities of water until it is thoroughly cooked in the form of a thick mush. It is then put into the remainder of the water or bouil- lon and subjected to streaming1 steam for two hours, after which, if the first heating was sufficient, it filters readily without the use of a hot-water filter, or the necessity of keeping it in the steamer during the filtering. The stirring rod must touch all parts of the bottom of the dish exposed to the flame, every few seconds during the preliminary heating, otherwise the agar will burn on and be spoiled. On some accounts it is best to begin operations with beakers rather than the enameled iron dishes. In this way all likelihood of using burned agar is avoided, since the moment the agar burns on the beaker cracks and the agar is spilled. For bacte- riological use agar should be clear, not cloudy or filled with unremoved precipitates. The writer now employs an autoclave and uses an agar flour procured from Lautenschlager or Merck (fig-33). If one has au au- toclave the preliminary heating of the agar in an open dish with a minimum quantity of water and all the subsequent stages may be dispensed with and the entire process carried on in the autoclave, unless it is known or suspected that media heated in the autoclave are less well adapted to the growth of par- ticular organisms than those pre- pared at 100° C. The amount of agar added to the culture fluid is usually i per cent. On the making of nutrient agar. Fig. 33* consult "Formulae," and the various standard text-books. Is there any difference in the appearance of colonies when grown at 5° to 10°, 15° to 20°, and 30° to 37° Observe the amount of precipitate that collects in the fluid in the V. For other observations as to growth on this substratum see " Gel
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