GROUND-AIR IN ITS HYGIENIC RELATIONS. 287 



by keeping the soil clean through good drainage, abolition of cess- 

 pools, and abundant water-supply. It would carry me too far if 1 

 were to analyze now to which of these measures the lion's part be- 

 longs ; I should have to enter upon many controversies, whicli I have 

 no time to fight out in this place ; but this is my conviction, which I 

 want to impress upon you, that cleanliness of the soil and diminution 

 of organic processes in the ground of dwelling-houses are most es- 

 sential. 



Many have considered these processes, and their effects on the 

 o-round-air, to be a mere hypothesis. This view lies now behind us, 

 and facts have been found proving their reality. Stimulated by the 

 investigations of Huxley and Haeckel, further researches have followed, 

 and shown that not only at the greatest depth of the sea, but also in 

 every porous soil, there are everywhere those beginnings of organic 

 life, belonofinsf neither to the animal nor vegetable kini>dom, mucous 

 formations, which are called Moneras and Protistes. Wlien I wrote 

 my part of the report on the cholera in Bavaria, in 1854, I pointed 

 out already that the air, not less than the water in the soil, ought to 

 be drawn into the circle of experimental investigations. Neither 

 others nor myself acted at once upon my suggestion, and it is only 

 during the last eighteen months that I have examined the ground-air 

 in the rubble-soil of Munich, regularly twice a week, for its vaiying 

 amount of carbonic acid. The results are surprising, and for the 

 future I shall have to trouble others and myself, not only with ground- 

 water, but also with ground-aii\ 



The place where the examination of the ground-air of Munich is 

 being carried on is rubble, without any vegetation, and the carbonic 

 acid increases with tlie distance from the surface. Agricultural chem- 

 istry has been aware, for a long time, that a clod of arable earth 

 which is rich in humus is a source of carbonic acid, but no one ex- 

 pected that, at times, so much carbonic acid should be met with in 

 sterile lime-rubble. A few feet under the surface there is already 

 as much carbonic acid as in the worst ventilated human dwelling- 

 places. 



I have found that the quantity of carbonic acid is smaller at fifty- 

 eight inches than at one hundred and fifty-six inches throughout the 

 year, the months of June and July excepted, when an inverse propor- 

 tion arises. But then there begins also, in the lower stratum, a con- 

 siderable increase, so that the upper stratum soon finds itself behind 

 again. This large quantity of carbonic acid in the ground-air of 

 Munich has been far surpassed in Dresden. Examinations have taken 

 place in that town under the authority of the Central Board of Public 

 Health. Prof. Fleck's diary proves that, at least at that spot where 

 his examinations took place, the quantity of carbonic acid was in 

 winter already nearly twice as great as in Munich in the month of 

 August. I might become jealous of Dresden, but we must often, 



