30 NATURE-STUDY REVIEW [16:1— Jan., 1920 



water timibles over rocks this mixture is already comparatively 

 high in oxygen content because of mixture with the air. 



Besides serving as producers of oxygen these plants further aid 

 in the purification of water by forming a film over the bed of water 

 courses. Before entering the earth to come out possibly else- 

 where, the water must filter through this film. In so doing many 

 impurities are prevented from entering to where the sun and open 

 air may be prevented from changing objectionable to desirable 

 qualities. The first water run through a commercial filter is never 

 as pure as that coming later when this film has had time to form 

 on the stirface of the sand. 



If purification of our water-supply were the only benefit gained 

 by man from this ooze and slime, we would have to admit its 

 importance. Further than this however, it fills a far-reaching 

 function in supplying food to innumerable forms which are fed 

 upon by large forms and which eventually make up the bodies of 

 the fishes which we ourselves eat. We can even carry the step 

 further and say that individual fish are at some time directly 

 dependent for food upon organisms in many ways similar to the 

 ooze which makes our footing quite unsafe. 



To many a boy the idea of a house made of cookies would be 

 the next thing to heaven, and practically an impossibility. In 

 practically every normal brook, however, a similar condition of 

 affairs exists for some of its inhabitants. Take a large stone from 

 almost any brook in the spring and shortly you may see red worms 

 (blood worms) crawling out of definitely formed masses of plant 

 material. To them the world has suddenly gone on a strike and 

 even though their homes are made of the material which makes up 

 their meals they are deprived of water and attempt to get back 

 where it is more to their liking. These forms make their houses 

 of this ooze and are directly dependent upon it for their food. In 

 turn they make excellent food for fishes. Pollywogs die in an 

 aquaritim containing nothing but water. Put a few ooz-covered 

 sticks in and leave them, and they live. They are dependent 

 upon the ooze for their existence and when they grow up we enjoy 

 eating their legs. Too many tadpoles would sweep the pond 

 fairly clear of ooze and so we see that one of the uses of frogs is to 

 keep these plants from multiplying to too great an extent. All 

 of these higher foims could not possible exist then were it not for 

 this ooze which combines materials not acceptable or usable as 



