844 
The Micro-oniunvims of the Soil. 
anxiety chemists now entertain as to a gradual diminution of this 
nutrient so essential to plants. 
To Hellriegel, Wilfarth, Wollny, Engelmann, Winogradsky, 
Warington, and Heraus may be attributed the most noteworthy 
experiments in this special line. In order to appi’eciate the impor- 
tance of their discoveries, I propose first to give a brief historical 
rhume of the study of fermentation. 
Historical Retrospect. 
Owing to the antiquity of the use of alcoholic beverages, the 
ferments entering into their production are best known, and this, 
added to the fact of their being larger and thus permitting of better 
examination, has been the determining cause of basing investigations 
and deductions upon their behaviour. 
The very fact that the art of cultivating the vine and making 
wine is attributed by the Egyptians to Osiris, the Greeks to 
Bacchus, the Israelites to Noah — the brewing of beer to Gambrinus 
— shows how old these discoveries must have been. The effects of 
fermentation are sufficiently striking to have called the attention of 
primitive man to them. The ancient tribes of Asia and Africa 
understood how to ferment not only grape juice, but also how to 
obtain alcoholic beverages from substances like starch, not directly 
fermentable. They used soured dough or beer-yeast as leaven for 
their bread, and knew how to prepare vinegar. The alchemists were 
wont to clothe their thoughts in such words as to make it difficult 
for us to decide what precise ideas they attached to the terms 
“Fermentation” and “Ferments,” which are so frequently found in 
their writings of the thirteenth to the fifteenth century. They even 
speak of the philosopher’s stone as “ fermenting ” unlimited quantities 
of lead and mercury into gold. 
In the fifteenth century Basil A^alentine in his Triumphal Car 
of Antimony claims that yeast employed in the preparation of 
beer communicates to the liquor an internal inflammation, thereby 
causing a purification and separation of the clear parts from those 
which are troubled ; but considers alcohol as ah’eady existing in the 
decoction of germinated barley. In 1648 Van Helmont declared 
fermentation the cause of all chemical action and spontaneous gene- 
ration, going so far as to giv'e directions for the production of mice, 
frogs, eels, tfcc. He clearly observed the production of a special gas 
(gas vinorum) during alcoholic fermentation, and stated that some- 
thing from the ferment passes into the fermentable substance, 
developing therein like a seed in the soil, thereby producing fermen- 
tation. 
Willis, an iMiglish physician, in 1659 claimed that all functions 
of life depended upon fermentation, and that diseases were but 
abnormal fermentations. Both he and Stahl regarded a ferment as 
a body endowed with a motion peculiar to itself, which it imparts 
to the fermentable matter. Stahl in 1697 advanced the following 
theory : “ Under the influence of the internal motion excited by the 
