G Tlie Use of a Simple Microscope. 



The genuineness of guano may also be learned through the 

 presence of certain flinty remains of organic bodies, which are 

 peculiar to the different deposits. Straw of wheat, oats, grass, 

 and many other vegetables, contain certain arrangements of flint 

 in their substance that are left entire after all vegetable matter 

 has become decomposed and washed away. These flinty and 

 imperishable remains of vegetable organisms that have existed 

 in the sea, and have either served directly as food for the pen- 

 guins, or previously filled the stomachs of fishes and molluscs on 

 which they have preyed, being deposited with the excrement 

 which forms the guano beds, are the characteristic features of the 

 best guanos. Says a late eminent Professor, "When examined 

 microscopically, a great abundance of beautiful silicious skeletons 

 of diatomacece are found amongst it ; and curiously enough, the 

 best samples of guano contain the greatest number of these 

 remains, which," says the late Professor Quekett, " were first 

 detected by my late brother in 1845." * " Now when we con- 

 sider," says the same writer," the vast amount of silica that must 

 be removed from the soil with the straw of wheat, barley, oats, 

 and other grasses, it must be evident that a supply of this 

 substance ought to be restoi'ed to the soil to insure good crops ; 

 hence it follows that the value of good guano as a manure may 

 depend not entirely upon its ammonia, lime, and potash, but in 

 a certain degree also upon the silica it contains." It is not 

 improbable that the superiority of farmyard manure may depend 

 very greatly upon the silica that the hay, corn, and straw contain, 

 which is hut sparingly appropriated by the animal. It may also 

 arise from a deficiency of silica that the straw of corn is often 

 weak, and breaks down under the weight of the ear. The exterior 

 surface of straw, canes, &c., derive their fine polish, as well as 

 their strength, from a layer of flint, as may be proved by boiling 

 them in nitric acid. 



For the process of obtaining these remains from guano, and 

 the flint from the stalks and leaves of plants, &c,, the reader is 

 referred to the valuable little work of Mr. Davies on the " pre- 

 paring and mounting objects for the microscope," t which is a 

 complete manual on the subject at a small cost. For an exami- 

 nation of these silicious remains the J-inch or \ of an inch 

 object-glass will be required, and a very accurate adjustment 

 of the light must be obtained to bring out their very beautiful 

 patterns in a satisfactory way. Of sand, loam, turf-ashes, and 



* Quekett's ' Histology,' vol. i. p. 59. 



t 'The Preparation and Mounting of Microscopic Objects,' pp. 151, by Thomas 

 Davies. 8vo., 2s. 6d. Hardwicke. 



