ZOOLOGY AND BOTANY, MIOKOSOOPY, ETC. 
129 
Every 10 or 15 days the water lost by evaporation should be replaced by 
sterilised water, and if the cultures drag, their growth may often be 
stimulated by adding a few drops of solutions A and B. 
(2) Culture of marine diatoms is easily done in sea-water. If, however, 
natural sea water cannot be obtained, it may be replaced by dissolving 
sea-salt 250 grm., sulphate of magnesium 20 grm., chloride of magnesium 
40 grm., in a litre of water, and when required for use adding 9 litres 
more. To the sea-water are added the solutions A and B, just as for 
fresh-water diatoms, and also a little Zostera leaf. 
(3) Pure cultures of diatoms are obtained by the fractional method, or 
by isolating a single healthy specimen. The former procedure is effected 
by mixing one drop of diatomiferous fluid with 100 ccm. of nutritive 
fluid, and diluting 1 ccm. thereof with 99 ccm. of fresh fluid. The last 
solution is then distributed in ten Freudenreich’s flasks and cultivated. 
In this way cultures of a single form may be finally obtained and further 
examined in a cell devised by Miquel (see p. 130). 
Dr. van Heurck then gives the methods and formulse used by the 
late Mr. C. Haughton Gill. The fluid from which Mr. Gill obtained the 
best results was composed as follows : — Solution A. Chloride of sodium 
10 parts, sulphate of sodium 5 parts, nitrate of potassium 2 • 5 parts, acid 
phosphate of potassium 2 • 5 parts, water 100. B. Filtered spring water 
100 vols., solution A 0 • 5 vol. To this solution is added a sufficient 
quantity of slaked lime to neutralise the acidity of the liquid, and a small 
quantity of precipitated silica. Finally, a small quantity of sterilised 
grass infusion or diatom broth, obtained by prolonged boiling of a largo 
quantity of fresh diatoms in water. After filtering the broth, it is pre- 
served in hermetically sealed tubes. Fine bone-scrapings were also 
added, and occasionally well washed grass roots. 
Though the foregoing gave very excellent results, Mr. Gill, in the 
last year of his life, adopted a fluid more like that of Miquel. This was 
a mixture of four different solutions : — 
Solution i. Pure crystallised phosphate of sodium 2 ; pure crystallised 
chloride of calcium 4 ; pure syrupy perchloride of iron 0*5; pure hydro- 
chloric acid 1 ; water 100. 
Solution ii. Pure crystallised sulphate of magnesium 4 ; pure crys- 
tallised sulphate of sodium 4 ; pure crystallised nitrate of potassium 4 ; 
common salt 8 ; bromide of potassium 0*2 ; iodine 0 # 2 ; water 100. 
Solution iii. Pure crystallised carbonate of sodium 4 ; water 100. 
Solution iv. Silicate of calcium, precipitated and washed, 25 ; 
water 75. 
Of each of these solutions 3 ccm. were taken and mixed with 1 litre 
of tap or sea water, and the mixture distributed in Erlenmayer’s flasks 
of 100-200 ccm. capacity, which were filled up to a height of 3 ccm. 
The flasks were plugged with cotton- wool, sterilised, and left for at least 
one week before being inoculated. Solution iii. has a double action, for 
it neutralises the acidity of the fluid and precipitates half of the calcium 
as useful carbonate. Mr. Gill was of opinion that the purity of the sub- 
stances used was highly important, especially of the perchloride of iron, 
the ordinary samples often containing arsenic, one of the most fertile 
causes of failure. Direct sunlight was harmful, and the culture flasks 
were placed [facing 'W.N.W., a screen of pale-green glass being inter- 
1898 K 
