512 SUMMARY OF CURRENT RESEARCHES RELATING TO 



aside, the eggs, if present, may be seen clinging to the unbroken side. 

 They are usually closely packed and sometimes extend over an area of 

 several square millimetres. The eggs are removed from the burrow by 

 means of a fine pipette to a shallow dish filled with clear water ; the 

 eggs are then separated from sand and transferred to small bottles of 

 sea-water ; eggs from the same burrow are kept in separate bottles. On 

 reaching the laboratory the eggs are placed in small dishes filled with 

 fresh sea-water, occasionally changed to keep the animals alive. The 

 animals were killed and fixed by means of Zenker's fluid, corrosive- 

 acetic mixture, Lo Bianco's chrom-osmic mixture, and osmic acid. The 

 specimens were preserved in 80 p.c. alcohol. The animals were killed 

 from time to time at different stages of development, fifteen series being 

 made. Numerous stains were used, the most satisfactory being haemaluni 

 counterstained with Congo red for the early stages, and Mallory's con- 

 nective-tissue stain for advanced stages that were fixed in Zenker's fluid. 

 Living material was examined with a stereoscope Microscope. 



Convenient Mode of Preparing Silicate Jelly.* — F. L. Stevens 

 and J. C. Temple describe their method as follows : First ascertain the 

 percentage of silicic anhydride on the sample of sodium silicate to be 

 used ; this consists in decomposing the silicate with hydrochloric acid, 

 precipitating the silicic acid, evaporating to dryness, washing until wash- 

 water contains no chloride, then heating to redness and weighing the 

 silicic anhydride. Enough should be made at once to last for several 

 years. After making the determination, dilute the silicate to be used 

 until the solution contains 4-5 p.c. of silicic anhydride. Next prepare 

 hydrochloric acid of such strength that 1 c.cm. neutralises 1 c.cm. of the 

 sodium silicate solution, using methyl-orange as an indicator (litmus, 

 phenolphthalein, and cochineal are not suitable). 



To 104 c.cm. of acid add slowly, constantly stirring the while, lOOc.cm. 

 of the sodium silicate solution, the excess of acid being used to prevent 

 coagulation during sterilisation. This solution is then tubed and 

 sterilised in an autoclave at 120° for 15 minutes. The silicic acid should 

 come out clear. If there be any turbidity it is due to a deficiency of 

 hydrochloric acid. The solution of silicic acid thus prepared constitutes 

 the base of the medium. To cause it to solidify to a jelly, add to a 

 tube of this base 1 c.cm. of a sterile concentrated solution of such salts as 

 may be desired, but in every case containing enough sodium carbonate 

 to a little more than neutralise the excess of acid present. In a few 

 minutes after the addition of the salt solution, the whole will be 

 solidified, giving a clear transparent jelly. If plate cultures be desired, 

 it is well to inoculate the base before the addition of the salts, since 

 after the medium starts to set, there is no time for proper mixing. If 

 slants be desired, the tubes must be placed in the proper position before 

 the medium sets. Prepared in this way, silicate medium is convenient 

 and efficient for the isolation of nitrite and nitrate organisms. Instead 

 of using sodium carbonate for neutralising, magnesium carbonate may 

 be employed, as when the jelly is prepared by dialysis. 



* Centralbl.Bakt., xxi. 2te Abt. (1908) pp. 84-7. 



