ZOOLOGY. 363 



scope calls attention to them. It is only necessary to take a clear glass 

 slide, and press a moistened finger gently on its surface, to bring several 

 starch grains into view. Nay, this will be the case after repeated washing 

 of the hands; but if you wash your hands in a concentrated solution of 

 potash, no grains will then be found on pressing the moistened finger on 

 the glass. This persistent presence of starch on our hands is not astonish- 

 ing svhen we consider the enormous amount of starch which must be rubbed 

 from our food and our linen every instant of the day; and when we con- 

 sider, on the one hand, the specific lightness of these grains, which enables 

 them to be so easily transported by the air, and, on the other hand, the 

 powerful resistance they offer to all the ordinary causes of destruction, one 

 may safely affirm that in every town or village a cloud of starch is always 

 in the air. 



And hereby hangs a tale. Starch is a vegetable substance, and, until a 

 very few years ago, it was believed to have no existence in the animal tis- 

 sues. But the great pathologist Virchow discovered that in various tissues 

 a substance closely resembling starch was formed, which he considered to 

 be a morbid product. The discovery made a great sensation, and many were 

 the ingenious theories started to account for the fact. At last it came to be 

 maintained that starch was a normal constituent of animal tissues; and 

 there is no doubt that investigators might easily find starch in every bit of 

 tissue they handled, since their fingers, as we have seen, are plentifully cov- 

 ered with grains. If, however, proper precautions be taken not to touch the 

 tissue with the fingers, nor the glass slide on which it is placed, no starch 

 will be found. It is because of the starch-clouds in our atmosphere that 

 grains are found on our persons and on almost every microscopical prepa- 

 ration. 



But are the starch-clouds all that the sunbeam reveals? By no means. 

 Some animals will be found there; not always, indeed, nor very numerously, 

 but enough to create astonishment. And these animals are not insects, dis- 

 porting themselves; they are either dead or in a state of suspended anima- 

 tion. A few skeletons of the infusoria, scales of the wings of moths and 

 butterflies, and fragments of insect-armor, may be reckoned as so much 

 dust; but there is also dust that is alive, or capable of living. You want to 

 know what that dust is? It is always to be found in dry gutters on the 

 house-tops, or in dry moss growing on an old wall; and Spallanzani, the 

 admirable naturalist to whom we owe so much, amazed the world with 

 announcing what old Leeuwenhoek had before announced, namely, that 

 these grains of dust, when moistened, suddenly exhibited themselves as 

 highly organized little animals the Rotifers and Tardigrades. Water is 

 necessary to their activity. When the gutter is dried up, they roll them- 

 selves into balls, and patiently await the next shower. If, in this dried con- 

 dition, the wind sweeps them away with much other dust, they are quite 

 contented; let them be blown into a pond, they will suddenly revive to ener- 

 getic life; let them be blown into dusty corners, and the.v will patiently 

 await better times. Such are some of the things found in the dust of a 

 sunbeam. In addition, a few spears of plants are also frequently found. 

 Knowing that many plants are fertilized by the agency of the wind, one 

 would naturally expect to find pollen grains abundant. Indeed, when we 

 consider how rapidly bread, cheese, jam, ink, and the very walls of the 

 room, if damp, are colored with mould, which is a plant; when we consider 

 how impossible it is to keep decaying organic substance free from plants 



