Biological Papers. 207 



the same time help to enrich the soil. These bacteria, beyond 

 question, increase the growth of alfalfa and Red clover. Indeed, it 

 is largely because of their presence in the soil that thesejcrops con- 

 tinue to flourish in Kansas. 



The root-tubercle bacteria are air lovers, and the soil must be 

 kept loose by cultivation or kept well shaded by the crop when wet, 

 or alfalfa, clover and the other legumes will not make their best 

 crop. Dressings of land plaster (gypsum) help these plants won- 

 derfully, but a porous soil is of the first importance. 



In the best soils the pore space equals one-half the volume of 

 the soil. In clay soils it is more ; in sandy soils, strangely enough, 

 it is less. As pore space is either air space or water space, the im- 

 portance of thorough water drainage, both surface and subsoil, is 

 evident. When the pore space is filled with air, the air-loving, ni- 

 trifying bacteria and the root-tubercle bacteria flourish best and 

 the heaviest crops are harvested. When the pore space is largely 

 reduced by plowing when the soil is too wet, or is filled with flood- 

 water, the air-hating, denitrifying bacteria rob the soil of its ni- 

 trates, and light crops are harvested. Puddled soil may be excellent 

 for dirt roads — indeed, makes the best roads when quickly dried, 

 with the pore space absent or largely reduced — but, on the farm, it 

 cannot grow valuable crops. 



5. Pathogenic bacteria are frequently found in rich soils. Among 

 the most numerous and dangerous of these is the bacillus of tetanus 

 (lockjaw). No wound received in stables is a safe wound. The 

 bacillus works in the wound; and lockjaw is caused by its excre- 

 tions, which are absorbed by the blood and carried to the nerve 

 centers. 



The bacteria which cause typhoid fever and tuberculosis are 

 likewise found in rich soils. The germs of typhoid fever may live 

 in soil impregnated with the excretions of a typhoid patient 456 

 days, and the germs of tuberculosis are found to be alive in soil 

 several weeks after having been added to it. All germs of this 

 character should certainly be destroyed before they are thrown 

 upon soil. 



Other disease germs are known to exist in the soil, some of bac- 

 teria and others of animals — the protozoa. It is probable that 

 some of the latter get into the drinking water and cause dysentery 

 and, possibly, appendicitis. 



The soils about buildings are being studied with the greatest 

 care, and, while very much remains for future work, enough is now 

 known to make it certain that water from deep wells, wells with 



