years during which time a number of scientific men discovered the 

 facts whicli constitute our present knowledge. 



It was the French chemist Berthelott who in 1885 suggested that 

 there might be in the soil certain organisms that were able to fix 

 atmospheric nitrogen. It was a German botanist, Hellriegel, who 

 m 1886 suggested that in the case of the leguminous plants this 

 property was possessed by the bacteria in the nodules. It was at 

 itothamsted that Lawes and Gilbert made the field trials and labora- 

 tory experiments that established the truth of these suggestions and 

 made them available to agriculturists. 



Glancing over what I have said, it becomes clear that we owe a 

 big debt of gratitude to these extremely minute but extremely abun- 

 dant bacteria. We are so accustomed to think of them as harmful, 

 as the cause of disease, on which medical men are never tired of 

 insisting, that the general public may be pardoned if they do not 

 recognise, or even know, of the vast utility of these microbes. 

 Indeed, the disease-producers are comparatively few, and we are 

 justified in saying that "All bacteria are useful and beneficial to 

 humanity, though some have become injurious by the accident of 

 their location within our bodies under certain circumstances." Life 

 as a whole could not continue without their aid. They do not 

 create life, perhaps, but they supply it with the necessary main- 

 tenance. It is by their means that the remains of dead animals and 

 plants are cleared away and the organic substances stored up in them 

 are returned to the air and soil in the form of inorganic matter, and 

 rendered once more available for the food of plants. 



As the prophet says, + " All flesh is grass" the sheep feed upon the 

 grass, we feed upon the sheep ; hence our food supply is in the last 

 resort dependent upon bacteria of the soil. 



PROTOZOA OF THE SOIL. 



It is known that at times and under certain circumstances a soil 

 Icses its nutritious character and becomes "sick" in spite of the fact 

 that it has received the usual amount of proper manure. 



This subject attracted the attention of Dr. Russell and Mr Hutchin- 

 son a few years ago (1909), t and they found that if such a soil be 

 partially sterilised by being heated to a temperature of about GOdeg. 

 Centigrade, or if it be treated with some volatile antiseptic such as 

 toluene, the number of bacteria normally present undergoes 

 remarkable changes. At first this number is greatly reduced, which 

 means the soil has lost in nutritive character. Then there is a very 

 marked increase. This rise in number sets in soon after the removal 

 of the antiseptic or after sterilisation has ceased, and the soil condi- 

 tions are now more favourable to the development of bacteria, and 



tBerthelot, "Fixation directe de 1'azote atmospherique libre par certain 

 terrains argileux." Comptes Rendues. 1885. 



Jlsaiah, chap, xl., verse 6. The prophet used the expression, of course, with an 

 entirely different connotation. 



tRussell and Hutchinson, "Journ. Agric. Science," vol. iii., 1909. 

 Proc. Roy. Soc., vol. 84, B., 1911, p. 165. 



