SANITARY RELATIONS OF THE SOIL. 469 



occupy the pores, and one in which the pores are quite filled with 

 water excluding the air. In the former case we may speak of soil- 

 moisture (JBodenfeuchtigkeit), in the latter of ground-water (Grund- 

 wasser). In many cases, but not universally, the transition from soil- 

 moisture to ground-water is very plainly indicated. 



The coincidence of the existence of ground-water with the preva- 

 lence of typhoid has been a constantly recognized fact since 185G. It 

 was discovered by Buhl, has been tested by Seidel according to the 

 law of probabilities, and has been followed out and confirmed down to 

 the present day by Port for the garrison at Munich, and by Ziemssen 

 for the avenues of the civil hospitals ; by whom it is shown that, when 

 the amount of ground-water is above the average, fewer, when it is 

 below the average, more, cases of typhus appear. The same law was 

 discovered by Virchow for the fluctuations of typhus in Berlin. The 

 lowest degree of saturation exists in Berlin during the later summer 

 and the fall, in Munich during the winter, and the seasons of typhus 

 are correspondingly different in the two cities : the latter part of sum- 

 mer and the fall in Berlin, winter in Munich. When the summer is 

 unusually dry at Munich, summer epidemics prevail there also. 



That the cause of these conditions is not the ground-water in and 

 of itself, but the moisture in the overlying strata and the processes 

 dependent upon it, is very plainly shown by two facts : first, that 

 some typhus-centers have a porous soil but no ground-water ; and, sec- 

 ond, that the level of the ground-water may be raised and depressed 

 by artificial means, as by damming, pumping, or draining, without any 

 notable influence being produced upon the prevalence of typhus. The 

 first case occurs in places where on account of the steepness of the 

 descent, or of any other cause, no ground-water collects on the lower 

 impervious strata ; the second case, where the level of the ground- 

 water is within the mark of the flood-height of a river. In Munich, 

 for example, it was necessary on one occasion, in order to carry on 

 some excavations in a part of the city near the Isar, to leave a gate in 

 the river open for several months, so that the water sunk more than 

 a metre. No increase of typhus was observed ; and when the gate 

 was closed, and the water was allowed to rise again to its original 

 height, the typhus did not diminish. A coincidence with the preva- 

 lence of typhus appears only when the variations in the level of the 

 ground-water proceed from the saturation or the drying-up of the 

 strata lying above it. I have always regarded the state of the ground- 

 water only as the best and plainly visible sign or index of the rhythm 

 of the soil-moisture in the overlying strata. 



Macpherson, Lewis, and Cunningham have shown beyond a doubt 

 that the cholera fluctuates in its home in India, like abdominal typhus 

 with us, inversely with the annual amount of rain and of saturation of 

 the soil. It behaves in the same way with us. The remarkable di- 

 vision of the cholera into a summer and a winter epidemic, which was 



