OUR ICE-SUPPLY AND ITS DANGERS. 679 



But let us return to our ice. He who is familiar with the researches 

 of Tyndall and other physicists on the structure of ice, knows how- 

 little we can be aware, from the simple inspection of a lump of clear 

 ice, beautiful as it is, how marvelously it is built up crystal by crystal 

 into the solid form we know so well. But if we turn a beam of sun- 

 light upon it, concentrated by a lens, the exquisite and varied steltate 

 figures which flash out within the solid mass as the magic touch of the 

 sunbeam releases the molecules of water from their crystal bonds, give 

 us enchanting glimpses of the still but half-won secrets of beauty 

 and of order with which Nature so fondly sports and still so cleverly 

 conceals. 



But the resources of the physicist do not suffice to conjure all its 

 secrets from a block of ice. It is left for the student of that phase of 

 Nature which we call life to discover that this very type of cold 

 impassive lifelessness may be fairly teeming, absolutely transparent 

 though it be, with whole families and races of living things — dormant 

 from chill it is true, but ready at the touch of warmth, and in the 

 presence of their food, to start on a career of growth and multiplica- 

 tion to which the increase in the world's populousness since the old Ice 

 age faded is but a poor and halting comparison. 



We can not follow the student of these lowly forms of life, which 

 have become entangled among the ice-ci*ystaLs, as he calls them back 

 from their torpor, sepai'ates them one by one, and patiently studies 

 their life-history. It is not enough to melt the ice and look at the 

 resulting water through the microscope. But he mingles the melted 

 ice with a transparent compound of gelatin and beef-tea, and puts 

 the whole in a warm place, and after a few hours or days, wherever in 

 this semi-solid gelatin a living germ from the ice had lain, a tiny 

 speck or rounded mass appears — a " colony " he calls it — which is 

 made up of thousands of the descendants of the old rescued and thawed 

 bacterial ancestor. And so the biologist can separate the species one 

 from another, cultivate them in various receptacles, and learn whether 

 they belong among man's friends or foes, 



A great deal of careful experiment has shown * that water in freez- 

 ing largely expels its coarser visible contaminations, and also that a 

 large proportion of the invisible bacteria which it contains may be 

 destroyed, even as many as ninety per cent. But still large numbers 

 may remain alive, for many species are quite invulnerable to the action 

 of cold. It has been found that in ice formed from water containing 

 many bacteria, such as w^ater with sewage contamination, the snow-ice 

 almost invariably contains many more living bacteria than the more 

 solid, transparent part ; so that the snow layer should be especially 

 avoided in ice obtained from questionable sources. 



Unfortunately, the bacteria which cause typhoid fever are not 

 readily killed by cold, and may remain alive for months, fast frozen in; 

 * See the New York " Medical Record," March 26 and April 2, 1687. 



