INFUSORIA. 1 5 



present when examined under the same magnifier ! (See the two points 

 m fig. 9.) 



An examination of this exact drawing has led me to make a calcula- 

 *on which leads to rather curious results : at a half millimetre from the 

 point, the diameters of the four objects represented are in thousandths of a 

 millimetre respectively, 3*4 ; 2*2 ; I'l ; 0*38. The corresponding sections in 

 millionths of a square millimetre are: 907-92 ; 380-13 ; 95*03 ; ii'34; or, 

 in round numbers, 908; 380; 95 ; II. 



If one bears in mind, which is much below the truth, that the pressure 

 exercised on the point must be proportional to the section, and admitting 

 that a pressure of 1 1 centigrams suffices to thrust in the sting of a wasp half 

 a millimetre, it will require more than 9 grams of pressure to thrust in a 

 needle to the same extent. In fact, this latter figure is much too small, for 

 we have not taken into account the advantage resulting from the elongated 

 shape of the rose thorn, which renders it more favourable for penetration than 

 a needle through a drop of tallow. 



It would be easy to extend observations of this kind to a number of 

 other objects, and the remarks I have just made on natural and artificial 

 points will apply incontestably to textures for example. There is no doubt 

 that the thread of a spider's web would far surpass the thread of the finest 

 lace, and that art will always find itself completely distanced by nature. 



We amused ourselves frequently by examining the infusoria which are so 

 easily procured by taking from some stagnant water the mucilage adhering 

 to the vegetation on the banks, or attached to the lower part of water lentils. 

 In this way we easily captured infusoria, which, when placed under a 

 strong magnifier, presented the most remarkable spectacle that one can 

 imagine. They are animalcules, having the form of transparent tulips 

 attached to a long stem. They form bunches which expand and lengthen ; 

 then, suddenly, they are seen to contract with such considerable rapidity that 

 the eye can scarcely follow the movement, and all the stems and flower-bells 

 are folded up into the form of a ball. Then, in another moment, the stems 

 lengthen, and the tulip-bells open once more. One can easily encourage the 

 production of infusoria by constructing a small microscopic aquarium, in 

 which one arranges the centre in a manner favourable to the development 

 of the lowest organisms. It suffices to put a few leaves (a piece of parsley 

 answers the purpose perfectly)* in a small vase containing water (fig. 10), 

 over which a glass cover is placed, and it is then exposed to the rays of 

 the sun. In two or three days' time, a drop of this water seen under the micro- 

 scope will exhibit infusoria. After a certain time, too, the different species 

 will begin to show themselves. Microscopical observations can be made on a 

 number of different objects. Expose to the air some flour moistened by water, 

 and before long a mouldiness will form on it ; it is \hzpenicillium glaucum, and 

 when examined under a magnifier of 200 to 300 diameters, cells are dis- 



* The infusion of parsley has the advantage of not sensibly obscuring the water. 



