August 2, 1889.] 



SCIENCE. 



79 



mer, so far as our present knowledge extends, the ground can 

 rarely serve as a favorable breeding-place. 



It is not, however, necessary that these organisms should multiply 

 in order to infect for a considerable time the ground : it is sufficient 

 if their vitality is preserved. As to this latter point, the reports of 

 different investigators are not altogether concordant. Such excel- 

 lent observers as Koch, Kitasato, and Uffelmann found that the 

 cholera bacteria, when added to faeces, or a mixture of fseces and 

 urine, rapidly diminished in number, and at the end of three or 

 four days, at the most, had wholly disappeared. In a mixture of 

 the intestinal contents from a cholera corpse with earth and water, 

 Koch found numerous cholera bacteria at the end of three days, 

 but none at the end of five days. On the other hand, Gruber re- 

 ports the detection of cholera bacteria in cholera dejecta fifteen 

 days old. The weight of bacteriological evidence, therefore, is op- 

 posed to the supposition that the bacteria of Asiatic cholera pre- 

 serve their vitality for any considerable time in the ground or in 

 the excreta. 



With respect to the bacilli which cause typhoid-fever, it has been 

 shown by Uffelmann that these may live in fseces, a mixture of 

 fasces and urine, and a mixture of garden earth, fseces, and urine, 

 for at least four and five months, and doubtless longer, although 

 they may die at the end of a shorter period. He also finds that 

 under these apparently unfavorable conditions some multiplication 

 of the bacilli may occur, although not to any considerable extent. 

 Grancher and Deschamps found that typhoid bacilli may live in the 

 soil for at least five months and a half. Unlike the cholera bac- 

 teria, therefore, the typhoid bacilli may exist for months at least in 

 the ground and in fascal matter, holding their own against the 

 growth of multitudes of saprophytes. This difference in the be- 

 havior of cholera and of typhoid germs is in harmony with clinical 

 experience. 



As regards other infectious bacteria than those which have been 

 considered, I shall only mention that tubercle bacilli, although in- 

 capable of multiplication under the ordinary conditions of nature 

 outside of the body, may preserve their vitality for a long period in 

 the ground, on account of their resistant character, and, further- 

 more, that the pyogenic cocci, on account of their considerably re- 

 sistant nature and their modest demands in the way of nutriment, 

 can be preserved and sometimes probably grow in the ground. 

 Indeed, the Staphylococcus pyogenes auretis has been found in the 

 earth by Lubbert. 



The conclusion which we may draw from the observations men- 

 tioned, is that in general the soil is not a good breeding-place for 

 most of the infectious bacteria with which we are acquainted, but 

 that it can retain for a long time with unimpaired vitality those 

 which produce spores or which offer considerable resistance to in- 

 jurious agencies, such as anthrax bacilli, typhoid bacilli, tubercle 

 bacilli, and the pyogenic cocci. 



In order to become infected with bacteria in or on the ground, 

 these bacteria must in some way be introduced into the body ; and 

 we must therefore now attempt to determine how bacteria may be 

 transported to us from the ground. So various and intricate are 

 the possibilities for this transportation, that it is hopeless to attempt 

 to specify them all. 



There occurs to us first the possibility of the conveyance of in- 

 fectious micro-organisms from the soil by means of currents of air, 

 • — a mode of carrying infection which has already been considered. 

 Here I shall only repeat that the wind can remove bacteria from 

 the ground only when the surface is dry and presents particles of 

 dust, and that the sole, perhaps the chief, danger is not that we may 

 inhale the infected dust. 



Manifold are the ways in which we may be brought into contact 

 with infectious bacteria in the ground, either directly or by means 

 of vegetables to which particles of earth are attached, by the inter- 

 vention of domestic animals, by the medium of flies or other in- 

 sects, and in a variety of other ways more or less apparent. 



An important, doubtless for some diseases the most important, 

 medium of transportation of bacteria from an infected soil is the 

 water which we drink or use for domestic purposes. From what 

 has been said, it is evidently not the subsoil-water which is danger- 

 ous, for infectious, like other bacteria, cannot generally reach this 

 in a living state ; but the danger is from the surface-water, and 



from that which trickles through the upper layers of the ground, 

 as well as from that which escapes from defective drains, gutters, 

 cesspools, privy-vaults, and wrongly constructed sewers or improper 

 disposal of sewage. I shall have something to say presently of 

 water as a source of infection, and shall not further elaborate here 

 the dangers of infection of drinking-water through contaminated 

 soil, — dangers which, especially as regards typhoid-fever, are 

 widely appreciated in this country, even if often imperfectly coun- 

 teracted. 



A point which has been much discussed, and one of interest, is 

 whether bacteria which are in the depth of the ground can come 

 to the surface. Two agencies, especially, have been considered by 

 some as capable of transporting bacteria from the depth to the 

 surface. One is ascending currents of air in the ground, and the 

 other is the capillarity of fluids in the minute pores of the ground. 

 The first of these suspected agencies must be unquestionably re- 

 jected, in view of the fact that even a few inches of sand is suffi- 

 cient to filter all of the bacteria out of the air, even when it is in 

 much more rapid motion than can occur within the ground. 

 Moreover, that degree of dryness which is essential for the detach- 

 ment of bacteria by air-currents is not likely to be present much 

 below the surface of the ground. The experiments which have 

 been made to determine to what extent bacteria may be carried 

 upward by the capillarity of fluids in the ground have not yielded 

 harmonious results, but the weight of evidence is opposed to the 

 belief that this is a factor 'of any considerable importance for this 

 purpose. 



From what has been said concerning the growth of pathogenic 

 bacteria in the soil, we shall not be inclined to attribute to the 

 multiplication and the motility of these organisms much influence 

 in changing their place in the ground. 



The somewhat sensational role assigned by Pasteur to earth- 

 worms, of bringing bacteria to the surface, cannot be wholly 

 ignored, and has received support from observations of Bollinger 

 regarding anthrax ; but it is questionable whether much impor- 

 tance is to be attached to this agency. 



Regarding the depth to which typhoid bacilli may penetrate in 

 the soil, the experiments of Grancher and Deschamps show that at 

 the end of five weeks they may reach a depth of sixteen to twenty 

 inches below the surface. As Hoffmann has demonstrated the 

 extraordinary slowness with which fluids and fine particles pene-. 

 trate the soil, it is probable that in the course of time a greater 

 depth than this may be reached. Indeed, Mace claims to have 

 found, in the neighborhood of a well suspected of infection, typhoid 

 bacilli, together with ordinary intestinal bacteria, at a depth of at 

 least six and a half feet below the surface. There are a number 

 of instances recorded in which there is good reason to believe that 

 turning up the soil, and cleaning out privies or dung-heaps in 

 which typhoid stools have been thrown, have given rise to typhoid- 

 fever, even after the infectious excreta have remained there a year 

 and more. 



It cannot be said that bacteriological investigations have as yet 

 shed much light upon a factor which plays a great role in epidemi- 

 ology, namely, predisposition to infection from the ground, accord- 

 ing to locality and time ; and this deficiency receives constant and 

 vehement emphasis from the localistic school of epidemiologists. 

 We can, however, readily understand that varying conditions, such 

 as temperature, moisture, porosity, quality of soil, may exert a con- 

 trolling influence in determining the behavior of infectious germs 

 in the soil, and the facility of their transportation to human beings 

 or animals. As regards that much-discussed question, the signifi- 

 cance of variations in the height of the subsoil-water in relation to 

 the prevalence of certain epidemic diseases, particularly cholera 

 and typhoid-fever, we now know that this cannot depend upon the 

 presence of bacteria in the subsoil-water itself, or in the capillary 

 layers immediately above it. It has been plausibly suggested, that, 

 with the sinking of the subsoil-water, fluids from infected cess- 

 pools, privy-vaults, and other localities, may more readily be drawn 

 into wells or other sources of water-supply, and that by the same 

 cause the surface of the ground becomes drj', so that dust-par- 

 ticles may be lifted by the wind. Other more or less plausible ex- 

 planations have also been offered, but it must be confessed that 

 our positive information on this point is meagre. There can, how- 



