122 FOOD. 



The objectionable inorganic constituents are those which give to 

 the water its " hardness." These are calcium carbonate, to which 

 " temporary " hardness is due, and calcium chlorid and sulphate, 

 and salts of magnesium, which account for " permanent " hardness. 

 Water is not considered to be " hard " unless it contains more than 

 ten grains of calcium carbonate or its equivalent per gallon (6.479 

 decigrams per 3.785 liters). Rain-water contains less than half a 

 grain (32.395 milligrams). To hard water gastric and intestinal 

 derangements are doubtless attributable, but the evidence that 

 vesical calculi or goiter are produced by it is far from convincing. 



It is, however, to the organic impurities which drinking-water 

 not infrequently contains that especial attention should be directed, 

 and more particularly to those in the form of disease-germs. 

 These organisms are the undoubted cause of cholera and typhoid 

 fever, and most probably of a form of dysentery called " amebic " 

 or "tropical." Each of these diseases is produced by its own 

 specific organism ; thus, that which produces cholera is Spirillum 

 choleras Asiaticce ; that of typhoid fever, Bacillus typhosus; and 

 that of tropical dysentery, Amceba dysenteries. These germs are 

 contained in the stools of persons suffering from these diseases, and 

 their stools not being disinfected, the germs gain access to drink- 

 ing-water either by a leaking privy-vault or in some other way, 

 and those who drink such water are liable to become infected. 

 Many instances of epidemics thus caused could be cited, but one 

 must suffice. One of the most striking epidemics of typhoid fever 

 was that which occurred in Plymouth, Pa., in 1885. The popula- 

 tion was between 8000 and 9000. Of this number, 1153 con- 

 tracted the fever, and 114 of these died. A careful investigation 

 showed that the water-supply of this mining-town had become in- 

 fected by the stools of a single case of typhoid fever. These 

 stools, in an undisinfected condition, had been deposited on the 

 ground during the winter, and it was not until spring, when the 

 snow melted and warm showers occurred, that these infected 

 dejecta were washed into the water-supply. The first case occurred 

 within two or three weeks after. This instance demonstrates not 

 only the infecting power of a single case of disease, but also the 

 resisting power which the typhoid bacillus possesses against cold, 

 for these stools had been frozen for several months. Indeed, from 

 laboratory experiments we know that the Bacillus typhosus retains 

 its vitality even after having been frozen for one hundred and three 

 days. 



The resistance of many other bacteria to low temperatures is a 

 well-established fact. The cholera germ is not killed at 32 c C. 

 (Koch). The bacillus of tuberculosis retains its vitality after an 

 exposure of forty-two days to the temperature of liquid air, 1 93 C. 

 (Swithinbank). Bacillus coli and other bacteria are not killed 

 after an exposure of ten hours to the temperature of liquid hydro- 

 gen, 252 C. (McFadyen and Rowland). 



