Deoxynucleic acid in some gametes and embryos 



Salt A: dissolve 20 g. of monobasic potassium phosphate, KH 2 P0 4 , in water to 

 make 100 ml. 



Salt D: dissolve 03 g. of Mohr's salt (Fe(NH 4 ) 2 (S0 4 ) 2 . 6H 2 0), 02 g. of sodium 

 chloride, 08 g. of manganese sulphate (MnS0 4 . 4.H 2 0), 4 g. of magnesium sulphate 

 (MgS0 4 . 7H 2 0), and 2 ml. of 1 n HC1 in water to make 100 ml. 



Tween 80 solution: dissolve 10 g. of Tween 80 (polyxyethylene sorbiton mono- 

 oleate) in water to make 100 ml. Store in a refrigerator. 



Cytidylic acid solution: dissolve 05 g. of cytidylic acid in water, adjust the pH 

 to 70 with about 2 m sodium acetate solution, and add water to make 100 ml. 

 Store in a refrigerator. 



Potassium acetate solution : dissolve 500 g. of potassium acetate in water to make 

 1,000 ml. 



Adenine-guanine-thymine solution: dissolve 02 g. each of adenine sulphate, 

 guanine hydrochloride, and thymine with the aid of heat in 10 ml. of 2 n HC1. Add 

 water to 100 ml. 



Thioglycolic acid solution: dissolve 1 g. of thioglycolic acid in water to make 

 100 ml. 



Vitamin solution: dissolve 05 mg. of folic acid and 5 mg. each of/>-aminobenzoic 

 acid, riboflavin, nicotinic acid and calcium pantothenate in 50 ml. of water. Store 

 under a preservative in a refrigerator. Prepare a fresh solution every month. 



Assay procedure 



The assay is carried out in lipless uniform test-tubes (100 x 8 mm. i.d.). To each 

 series of tubes the standard vitamin solution is added in the following amounts : 

 00, 01, 02, 04, 06, 08 and 1 o ml. each with an error of not more than 2 per 

 cent. Each level is set up in duplicate. The extract of the sample to be assayed is 

 similarly added to a series of tubes in the following amounts: 0*2, 0-4, o*6 and o*8 

 ml., also in duplicate. All tubes are diluted to 1 o ml. with distilled water and i-o ml. 

 of the basal medium is added. The tubes are shaken, covered with glass or aluminium 

 caps, autoclaved at 120 G. for 5 min., cooled to room temperature, and inoculated 

 with one drop of the immediately previously prepared inoculum suspension. To two of 

 the four tubes containing o ml. of standard no inoculum is added. These tubes are 

 used as blanks in the turbidimetric determination of growth. All tubes are incubated 

 at 37 C. for 24-36 hr. 



Determination of response 



The tubes are shaken and the turbidity is read in a photometer (e.g., Lumetron 

 402 C, Photo volt Corporation, 95 Madison Avenue, New York, 16) at A = c. 650 rmt. 

 The microcuvettes are filled with a pipette and emptied with a piece of plastic tub- 

 ing connected to a suction pump. 



Calculation of results 



A standard dose-response curve is prepared by plotting the average of the turbidity 

 values found at each level of the deoxynucleoside standard against the amount of 



