SANITARY RELATIONS OF THE SOIL. 337 



live must exercise a very great influence upon them ; and, so far as this 

 medium is the soil, we have to investigate the conditions which it offers 

 for the growth of these organisms and the communication of them to 

 men. It must be admitted that mycology has so far given us very 

 little light on this point, and many problems respecting it are still 

 waiting to be solved ; but it is already well established that hygiene 

 as well as agriculture has much to do with the ground. 



Some advance had already been made in the investigation of the 

 hygienic relations of the soil before molds were mentioned as causes 

 of infectious diseases. The simple observation that such diseases oc- 

 curred or did not occur under certain conditions of the soil was enough 

 to provoke this. It had already become possible, without knowing the 

 more immediate causes, to make an unhealthy soil healthy. The best- 

 known examples of this kind are given in the cases of intermittent 

 fevers and malarial soils, in which the deleterious properties have been 

 wholly or partly remedied by drainage and the drying up of the sub- 

 soil, and the fertilization and cultivation of the surface. Tommasi- 

 Crudelli has a remark of the highest interest in his recent work on the 

 malaria of Rome and the former drainage of the Roman hills, to the 

 effect that the ancient Romans suffered much less from fevers than 

 the Romans of after-times and of to-day. The archaeologist De Tucci 

 having called attention to some underground canals of a peculiar kind, 

 called cuniculi, in the Roman hills, Tommasi examined them, and 

 found that they were designed exclusively to drain the hills, and that 

 they were now choked up and inoperative. Formerly, he thinks, they 

 were so familiar that the ancient Roman writers did not think it worth 

 while to speak of them ; they passed into forgetfulness during the 

 irruptions of the barbarians and the middle ages, and have now had 

 to be discovered anew. 



Measures directed against other infectious diseases that depend on 

 the soil have not been without results, although the specific causes of 

 the diseases are not known. 



What are the conditions of soil favorable to epidemics ? 



It is an old experience that certain infectious diseases have their 

 favorite seats in the so-called alluvial soils, in lands subject to over- 

 flow. Alluvial soil consists chemically and geognostically of substan- 

 tially the same mineral matters as the compact mountain-masses, from 

 the disintegration of which it has originated except that its physical 

 aggregation is essentially different ; and it is distinguished from rock- 

 soils by the great permeability for air and moisture arisiiJg from its 

 great porosity, that is, from the spaces in which air and water, as well 

 as organic matters, can find place. There are also kinds of rock which 

 are very porous, and their behavior is not materially different from 

 that of alluvial soils, as is shown by the cholera-epidemics in the Isl- 

 and of Malta. 



In common life we can hardly conceive the extent of the porosity 

 vol. xx. 22 



