38 



LECTURES ON BIOLOGY 



various animalcules which owing to their frequent occurrence 

 in the lichen on roofs or in the dirt of gutters are comprised 

 in the name of ' gutter fauna.' As early as the end of the 

 seventeenth century the famous Dutch zoologist Leeuwenhoek 

 discovered by means of a home-made microscope that in the dirt 

 of gutters or lichen-covered rocks and trees there lived minute 

 organisms which were able to dry up into insignificant particles 

 of dust and come to life again when moistened by the rain. 

 Recent investigations have removed all doubts that were long 

 cast upon this discovery, and also demonstrated the existence 

 of other similar organisms. 



If, for instance, 

 we place the dust- 

 crust of dried moss 

 on a piece of glass 

 and examine the 

 whole under the mi- 

 croscope we shall see 

 after a short time 

 that some of the 

 seeming grains of 

 sand begin to swell, 

 extend, and show 

 distinct signs of in- 

 dependent motion 

 (fig. 10). Soon the 

 stillness of death be- 



FIG. 10. BEAR-ANIMALCULES (MdCroUotUS hufeldndl), COm6S ^placed by 

 ALIVE, AND IN A STATE OF DRY-COMA. actlVC life, and nU~ 



merous awkward 



bear-animalcules, dainty rotatoria and minute amoebae crawl and 

 swim about in search of food. But no sooner do we let the water 

 evaporate than the movements of these strange organisms 

 become slower and slower, their forms shrivel up, and we observe 

 once more nothing but particles of dust and sand. 



The power of resistance of these minute organisms is extra- 

 ordinary. Particles of dust w T hich had been kept dry several years 

 developed into Wheel and Bear-animalcules and even minute 

 crustaceans. They seem equally insensible to heat and cold and 



