Securing Food 33 



trolled laboratory conditions. The method originated by Miquel (1897) 

 and modified by Allen and Nelson ( 19 10, 19 14) consists of adding certain 

 nutrient salts to seawater, sterilizing, and inoculating with a single 

 species of diatom. Two solutions are prepared separately: 



table 8. Preparation of Miquel solution. 



Solution A. 



Potassium nitrate 20.2 gm. 



Distilled water 100 cc. 



Solution B. 



Calcium chloride (CaCb 6H2O) 4 gm- 



Sodium phosphate, secondary, 



Crystals (Na 2 HP0 4 12H2O) 4 gm. 



Ferric chloride (melted) (FeCl 3 6H 2 0) 2 cc. 



Hydrochloric acid (HO) concentrated 2 cc. 



Distilled water 80 cc. 



Dissolve calcium chloride in 40 cc. of distilled water and add the 

 hydrochloric acid. In a separate beaker dissolve the sodium phosphate 

 in 40 cc. of distilled water, add the melted ferric chloride, and slowly mix 

 the two solutions. To prepare Miquel's solution add 2 cc. of solution A 

 and 1 cc. of solution B to one liter of seawater. Sterilize by bringing 

 just to the boiling point. Cool and decant or filter off the slight pre- 

 cipitate, separating the amount obtained into two 1 liter flasks. Shake 

 vigorously to aerate. The prepared medium is poured into sterile, short- 

 necked, wide-mouthed flasks of 125 cc. capacity and is covered with 

 inverted beakers. The flasks should be only about % full so tnat the 

 proportion of air surface to the volume of the liquid is large. The flasks 

 are inoculated by adding 6 to 8 cc. of an old culture of diatoms and are 

 placed in front of a window but are protected from the direct sunlight. 

 They should be shaken at least once a day. 



The Miquel's seawater may be modified by adding garden soil extract 

 which is known to have a stimulating effect on the growth of diatoms 

 (Gran, 1931, 1932, 1933). To prepare the extract put 500 grams of 

 garden soil in a flask, add 500 cc. of water and autoclave for 20 minutes 

 at 15 lbs. pressure. Filter, sterilize again, and keep in the refrigerator. 

 Add 1 cc. of soil extract to each liter of prepared Miquel's seawater. 

 Experiments carried out by Gran (1932) at Woods Hole show that the 

 synthetic Ferri-ligno-protein compound of Waksman (1932) which in its 

 chemical characteristics corresponds closely to the "humic" substances 

 of the soil, gives the same stimulating effect on the growth of the plank- 

 ton diatoms as the soil extract. 



Needless to say, in dealing with diatom cultures the same precautions 

 must be taken as are usually observed in bacteriological work. The 

 cultures grow best at about 15 to 16 C. 



