362 



SCIENCE 



[N. S. A'OL. XLIX. No. 1267 



supply in the earlier stages of growth may 

 stunt the plant so that absorption in the later 

 stages is much less than would occur with a 

 normal plant. 



D. E. Ho AG LAND 



Division or Agricultural Chemistry, 

 Univeksitt of California 



unheated egg-yolk media 

 Foe some years the writer has been using 

 jinheated ^g-yolk media and has found them 

 espeoially valuable in studying one of the 

 foulbroods caused by an organism (Bacillus 

 larvce) which offers considerable difficulty in 

 its cultivation. In a paper " Further Studies 

 on American Foulbrood " to be published in 

 the Journal of Agricultural Research, refer- 

 ence is nlade to the employment of such media 

 successfully in the study of this species. Be- 

 lieving that the fact might be of interest to 

 those studying diseases caused by organisms 

 for the cultivation of which unheated animal 

 products are being employed and possibly also 

 to those using heated egg media in their work, 

 the teehnic used in the preparation of these 

 media is given at this time. 



These are prepared by adding simply a 

 sterile aqueous suspension of egg-yolk to the 

 different media commonly used in the labora- 

 tory. The egg suspension is obtained as fol- 

 lows: After being disinfected the shell of the 

 egg is broken the white poured off and the yolk 

 dropped into a flask containing about TO c.c. 

 of sterile water. By agitating the flask a uni- 

 form suspension of the yolk material is ob- 

 tained. This is then transferred to sterile 

 tulbes by pipetting, and stored until needed. 

 On standing the suspension separates into a 

 more or less translucent supernatant fluid and 

 an opaque lighter yeUow-eolored sediment. 

 , In preparing the egg media about 1 c.c. of 

 the egg-yolk suspension is added to each 5 c.c. 

 of the base medium. If only the supernatant 

 fluid is used a clearer medium will result. 

 Egg agar has been the most useful of these 

 media in the work referred to. The base 

 should be at least 1.5 yer cent, agar and after 

 being liquefied should be cooled to between 

 45° and 50° C. before the suspension is added. 



Tubes may be inclined and stored until needed. 

 The medium may be inoculated and plates 

 made, or sterile plates may be poured. Al- 

 though the pipetting of the sterile suspension 

 rarely results in contamination of the media, 

 if convenient to do so, it is well to test them 

 for sterility after this step is taken. The ^g 

 suspension itself is a medium of some differ- 

 ential value. 



Eggs known to be recently produced are pre- 

 ferable for the egg-yolk susipension, although 

 those obtained from the market labelled 

 " strictly fresh " have usually been satisfactory. 

 The shell is disinfected convenientlj' by im- 

 mersing the egg in a suitable solution for a 

 few minutes. A 1: 1,000 mercuric chloride 

 one is satisfactory for the purpose. Alcohol 

 and solutions of carbolic acid and formalin 

 have been used but the latter two unless gloves 

 are employed are unpleasant to the hands. 

 After removing the egg from the solution, the 

 shell is broken about one end and removed with 

 forceps sterilized conveniently in the direct 

 flame. The white being poured off the limit- 

 ing membrane of the yolk is broken and the 

 yolk material is poured into the flask contain- 

 ing the sterile water. The degree of trans- 

 parency of the sui>ematant fluid depends some- 

 what upon the amount of water used ii 

 making the suspension. Occasionally con- 

 taminations are encountered. These are usu- 

 ally detected by changes in the appearance 

 of the suspension following incubation. 



G. F. White 

 Bureau of Entomology, 

 Washington, D. C. 



SCIENCE 



A Weekly Journal devoted to the Advancement of 

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 ceedings of the American Association for 

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