August 2, 1889.] 



SCIENCE. 



81 



As regards the vital question of water-supply, it may be stated 

 as a general principle that no hygienic guaranty can be given for 

 the purity of surface-water which has not been subjected to a 

 proper system of filtration, or for the purity of spring or well water 

 fed from the subsoil, unless such water is protected from the pos- 

 sibility of infection through the upper layers of the soil or from the 

 air. This is not saying that water which meets certain chemical 

 and biological tests, and which is so situated that the opportunities 

 for its contamination appear to be absent or reduced to a mini- 

 mum, is not admissible for the supply of drinking-water ; but the 

 possibility of infection can be removed only by the fulfilment of the 

 conditions just named, and upon these conditions the hygienic 

 purist will always insist. 



Unfortunately we have at present no domestic filters which are 

 satisfactory; and most of those in common use are worse than 

 none, as they soon furnish a filtrate richer in bacteria than the 

 original water. The only effective method of water-filtration for 

 the general supply is by means of large sand-filters, such as are in 

 use, with excellent results, in Berlin and some other cities. These 

 require skilled attention. I cannot on this occasion discuss the 

 construction or working of these filters, but would refer those who 

 are interested to the full and careful investigations of the Berlin 

 filters by Wolffhiigel and by Plagge and Proskauer. 



What is accomplished by these artificial sand-filters is accom- 

 plished under natural conditions also by the ground, which fur- 

 nishes a subsoil-water free from micro-organisms ; and to obtain 

 pure water we have only to devise means by which this subsoil- 

 water may be secured without the chance of contamination. Just 

 as the water which has passed through the sand-filters is collected 

 in suitable reservoirs, and is distributed in pipes which do not 

 admit contamination from without, so, by mdans of properly con- 

 structed artesian or driven wells, we may secure the naturally 

 filtered subsoil-water with the same freedom from the chances of 

 infection. 



It is well to bear in mind that no biological or chemical tests of 

 water can replace those measures which have been mentioned as 

 necessary to secure purity of water-supply. These tests are of 

 value only when applied with proper precautions, and with due 

 consideration of the special circumstances of each case for which 

 they are employed. There has been much profitless discussion as 

 to whether greater significance is to be attached to the chemical 

 or to the bacteriological examination of water. Each has its own 

 special field of application, and in this the one cannot replace the 

 other method. The bacteriological examination has for hygienic 

 purposes the advantage that it may enable us to detect the specific 

 agents of infection in the form of micro-organisms, as has already 

 been done for cholera bacteria and typhoid bacilli ; but this is a 

 comparatively rare result, and does not at present afford a wide 

 field of application for this method. The significance of the bac- 

 teriological test is to be based more frequently upon the fact that 

 it concerns itself with the same class of micro-organisms to which 

 some of the recognized, and doubtless many of the undiscovered, 

 infectious agents belong, and from the behavior of which, in some 

 respects, conclusions can be drawn as to the behavior of the patho- 

 genic organisms. Thus the bacteriological test is the only one 

 which enables us to judge correctly of the efficacy of those methods 

 of filtration of surface-water and of construction of wells which in- 

 sure purity of water-supply. The points of view from which we 

 can estimate correctly, according to our present knowledge, the 

 relative merits and fields of application of the chemical and of the 

 bacteriological methods of water-examination, have been clearly 

 indicated by Plagge and Proskauer, and by Wolffhiigel. The 

 theme is one beyond the limits or the scope of this discourse ; and 

 I have referred to it chiefly to emphasize the fact that we cannot 

 rely upon chemical or bacteriological tests of water to the exclu- 

 sion of those protective measures which have been m entioned 

 although I do not intend to imply that each of these tests, when 

 properly employed, does not afford important information and is 

 not of great value in many cases. 



I have already taxed so largely your time and patience, that I 

 must pass over with brief mention the food as a source of infection. 

 Unlike those external sources of infection which we have hitherto 

 considered, many articles of food afford an excellent nutritive 



medium for the growth of a number of species of pathogenic 

 micro-organisms, and in many instances this growth may be- 

 abundant without appreciable change in the appearance or taste of 

 the food. 



When we consider in how large a degree the certainty and the 

 severity of infection with many kinds of pathogenic micro-organ- 

 isms depend upon the number of such organisms received into the 

 body, we can appreciate that the danger of infection from food 

 which contains a mass of growing pathogenic bacteria may be 

 much greater than that resulting from the reception of infected) 

 water or air, — media in which infectious organisms are rarely 

 present in other than a very dilute condition. The entrance into 

 the body of a single infectious bacterium with the inspired air is, at 

 least in the case of many diseases, not likely to cause infection ; 

 but let this bacterium fall upon some article of food, as, for in- 

 stance, milk, where it can multiply in a short time at a favorable 

 temperature many thousand-fold, and evidently the chances of in- 

 fection become vastly increased. 



Among the various agencies by which infectious organisms may 

 gain access to the food may be mentioned the deposition of dust 

 conveyed by the air ; earth adhering to vegetables ; water used in 

 mixing with or in the preparation of food, in cleansing dishes,^ 

 cloths, etc. ; and contact in manifold other ways with infected- 

 substances. 



Fortunately a very large part of our food is sterilized in the pro- 

 cess of cooking shortly before it is partaken, so that the danger of 

 infection from this source is greatly diminished, and comes into- 

 consideration only for uncooked or partly cooked food, and for 

 food which, although it may have been thoroughly sterilized by 

 heat, is allowed to stand for some time before it is used. Milk, in 

 consequence of its extensive use in an unsterilized state, and of the 

 excellent nutritive conditions which it presents to many pathogenic 

 bacteria, should be emphasized as especially liable to convey certain 

 kinds of infection, — a fact supported not less by bacteriological 

 than by clinical observations. Hesse found that also a large num- 

 ber of ordinary articles of food, prepared in the kitchen in the usual 

 way for the table, and then sterilized, afford a good medium for 

 the growth and preservation of typhoid and cholera bacteria, fre- 

 quently without appreciable change in the appearance of the food.. 



Upon solid articles of food, bacteria may multiply in separate 

 colonies, so that it may readily happen that only one or two of 

 those who partake of the food eat the infected part ; whereas with 

 infected liquids, such as milk, the infection is more likely to be 

 transmitted to a larger number of those who are exposed. 



In another important particular the food differs from the other 

 sources of infection which we have considered. Not only the 

 growth of infectious bacteria, but also that of bacteria incapable of 

 multiplication within the body, may give rise in milk and other 

 kinds of food to various ptomaines, products of fermentation, and 

 other injurious substances, which, when ingested, are likely to 

 cause more or less severe intoxication, or to render the alimentary 

 tract more susceptible to the invasion and multiplication of genu- 

 inely infectious organisms. 



It is plain that the liability to infection from food will vary ac- 

 cording to locality and season. In some places and among some 

 races the proportion of uncooked food used is much greater than 

 in other places and among other races. In general, in summer 

 and in autumn the quantity of fruit and food ingested in the raw 

 state is greater than at other seasons ; and during the summer and 

 autumn there is also greater danger from the transportation of 

 disease-germs from the ground in the form of dust, and the amount 

 of liquids imbibed is greater. The elements of predisposition, ac- 

 cording to place and time, upon which epidemiologists are so fond 

 of laying stress, are not, therefore, absent from the source of infec- 

 tion now under consideration. 



I have thus far spoken only of the secondary infection of food 

 by pathogenic micro-organisms ; but, as is well known, the sub- 

 stances used for food may be primarily infected. Chief in impor- 

 tance in the latter category are the various entozoa and other para- 

 sites which infest animals slaughtered for {pod. The dangers to 

 mankind resulting from the diseases of animals form a separate 

 theme, which would require more time and space than this address 

 affords for their proper consideration. I shall content myself oa 



