86 GENEEAL HISTORY OF THE INFUSOKIA. 



the living organisms mainly composing it may have the power of self- 

 development in the aii\ 



Uses of Diatomaceous Deposits. — The utility and possible and probable 

 piu-poses of these minute organisms to mankind have not yet met with due 

 consideration. Their relation to the soil, in which they are so abundant, 

 and their influence on its fniitfulness are matters only incidentally reflected 

 on by authors. " Sufficient attention," remarks Prof. Gregory (J. M. S. 

 1855, p. 2), '' has not yet been paid to the fact of the invariable presence of 

 Diatomea) in all earths in which plants are found. Ehrenberg, in his Ml- 

 Jcrogeohgie, has established the fact as a universal one, and pointed out the 

 important bearing it has on the growth of the soil. Indeed, it is difficult to 

 imagine a more effectual agent in the transference of silica from the waters 

 to the solid earth than the growth of Diatomeae, the shells of which are as 

 indestructible as their multiplication is rapid. Ehrenberg is of opinion that 

 they live in the soil as well as in water ; and the constant presence of 

 moisture in the soil renders this conceivable, ^ilthough tlie proportion of 

 silicious matter dissolved in ordinaiy water is but small, it is e\idently 

 sufficient to supply the shells of millions of Diatoms in a veiy short time ; 

 and it is therefore probable that, as fast as it is extracted from the water by 

 them, it is dissolved from the rocks or earths in contact with the water, so 

 that the supply never fails." 



Mr. Roper has also suggested, from the consideration that the best samples 

 of guano contain the greatest number of these sUicious skeletons, which 

 doubtless serve to replace the large amount of silica abstracted from the soil 

 by the cereal crops, that it is probable that the deposits of many of our 

 rivers would have a beneficial efl'ect if applied to the land ; and it rests vdth 

 the microscopist to point out the most favourable localities for obtaining 

 them. Ehrenberg notices an instance where this has been done in Jutland, 

 where a blue sand abounding in calcareous and sihcious shells is collected, 

 and greatly increases the fertility of the arable soil to which it is aj^plied ; 

 and Prof. Bailey also states that the mud of Newhaven harbour is used as a 

 fertilizer, and is found to contain 58*63 per cent, of silica. The author 

 last-named has moreover adduced instances to prove that the great fertility 

 of the rice-fields of South Carolina is mainly due to their richness in Diato- 

 maceous remains. This notion is strengthened by the examinations of 

 Ehrenberg, and by the commonly observed fact of the occurrence of Diatomeas 

 about the roots of plants, especially of the cereals, which demand a large 

 supply of silicious material to construct their stems. 



Dr. Hooker {ojy. cit.) contends that the abundant Diatomaceous deposits of 

 the South Pole supply ultimately the means of existence to many of the 

 smaller denizens of the ocean, and that they keep up that balance between 

 the animal and the vegetable kingdom which prevails through all other lati- 

 tudes. He adds that they probably piuify the vitiated atmosphere, just as 

 plants do in a more temperate region. 



In the arts, the remains of Diatomaceous shells, as the chief ingredients in 

 certain deposits, are brought into use as polishing-powder under the name of 

 Tripoli, and also, as an extremely fine and pure silicious sand, in the manu- 

 facture of porcelain. The powder called Tripoli has various origins, and 

 differs in the microscopic organisms it contains. Species of Melosira especially 

 abound — for instance, of Melosira varians. Ehrenberg informs us that the 

 Tripoli of Jastraba in Hungary and that from Cassel resemble each other in 

 their component species. 



A very remarkable application of a deposit of Diatomeae is its use as 

 an article of food, imder the pressure of want, by the wretched inhabitants of 



