174 



SCIENCE-GOSSIP. 



bleaching of the material has been accomplished, 

 the vessel and its contents should be set aside to 

 cool. On no account should cold water be allowed 

 to come into contact with them until the tem- 

 perature has fallen below the boiling-point of 

 water, or a violent explosion will assuredly follow- 

 It is better, when somewhat cool, to pour the 

 contents of the vessel into another of clean rain 

 water, and, after perfect subsidence of the solid 

 matter, the liquid may be poured off, and a fresh 

 portion added, and this may be repeated so long as 

 any acid taste remains. It is desirable to get rid 

 of this persistent acidity as soon as possible. I 

 therefore always after one or two washings, add 

 sundry lumps of common soda to the preparation 

 until all effervescence ceases. Then I allow it to 

 remain quite undisturbed until next day. Strangely 

 enough, although the solid contents of vessel were 

 white, and the water colourless, they will now be 

 found, the first less white, and the latter almost 

 black, and this effect will be the result of several 

 repetitions of the operation. 



It may be supposed that the whole process has now- 

 been completed, and occasionally such may be so ; 

 but more often than not, upon placing a portion of 

 the preparation upon a glass slip under the micro- 

 scope, it will be found that, although the individual 

 diatoms are tolerably clean, they are so much 

 mixed with mineral matter that the whole process 

 must be repeated until the diatoms— clean and 



bright — sponge spicules and gemmules and sand 

 alone remain. 



It is almost impossible here to give instructions 

 as to the best method of dealing with every 

 individual case, as each material requires some- 

 what different treatment. It may, however, be 

 stated that, as a rule, the foreign matter mixed 

 with the diatoms consists of lime and its com- 

 pounds, or of extremely fine particles of silicious 

 matter. The lime may be removed either by 

 hydrochloric acid, or by repeated washings with 

 cold pure rain or distilled water. Lime dissolves 

 but very sparingly in hot water, more readily 

 in cold, and after the preparation has been 

 allowed to stand for a day, the clear water will 

 have become milky. This cloudy fluid must be 

 poured off from the sediment, and clear water 

 added, day after day, until no further cloudiness 

 is to be observed. This is a very tedious process, 

 and the operator will probably prefer the use of 

 hydrochloric acid. When all has been done it is 

 almost invariably better to. give the preparation a 

 boil with carbonate of soda. Bring it to a boil, 

 not much more ; three or four minutes will then 

 suffice, for if longer continued the diatoms will 

 certainly suffer. A lump of common soda about 

 the size of a walnut will be sufficient for one pint 

 of water if the preparation be tolerably clean, for 

 half-a-pint if it be somewhat dirty. 

 {To be continued.) 



CHAPTERS FOR YOUNG NATURALISTS. 



THE INFINITELY LITTLE. 



By J. O. Symes, M.D. 



{Continued f;om page 141.) 



been a very doubtful benefit, and such will 

 find some consolation in the fact that whilst 

 there is only one known species of germ capable 

 of making alcohol, there are many capable of 

 spoiling it. In a recent number of a trade 

 journal there was an article entitled, "Micro- 

 organisms causing Diseases of Beer," and a goodly 

 list was appended. These are .the temperance 

 reformers of the World of Germs. Chief amongst 

 them is the acetic acid organism, whose peculiar 

 function it is to convert alcohol into vinegar. In 

 countries where wine is plentiful and exceedingly 

 cheap, vinegar is made by adding this germ to the 

 wine and allowing it to undergo acetous fermenta- 

 tion. In England, however, vinegar, like beer, is 

 made from malt. Alcoholic fermentation is first 

 excited by the addition of yeast, and then the new 

 vinegar-producing microbe, called in the trade 

 " rape," is introduced, and the conversion of the 

 malt is complete. There are many other instances 



ZOOMING now to the fermentative species. The 

 ^ one which most readily presents itself to our 

 notice is the yeast-germ. Yeast consists of a mass 

 of microscopic cells, or germs, each of which has the 

 power of converting a solution of sugar and water 

 into alcohol. The yeast cell on gaining access to a 

 sugary solution at once begins to digest it, and the 

 result of that digestion is to convert the compound 

 into alcohol. The cells when dry are cabable of 

 being floated about in the air, and are indeed con- 

 stantly present there, thus accounting for the fact 

 that any sweet syrupy liquids left exposed soon 

 undergo fermentation. At first it was not known 

 which particular species of germ caused the 

 changes just described ; but when once the species 

 had been isolated it was carefully cultivated and 

 its energies devoted to man's use. We can now 

 buy yeast by the ounce or pound, a curious way of 

 retailing germs. The discovery of this alcohol- 

 producing microbe may appear to many to have 



