October 13, 1892] 



NATURE 



577 



it into a product which ceases to sustain it, but can nourish a 

 lower class of organisms whereby concomitant fermentations 

 arise, whose united effects are frequently such as to completely 

 modify those produced by each separately ; and for this reason 

 have the specific actions of some ferments either totally escaped 

 observation or have been misconstrued. Every succeeding year 

 brings additional proof of the important role played by these 

 minute organisms, and to such an extent, especially, has this 

 been the case in connection with the rendition of available 

 nitrogen, that there are good reasons to believe that a clearer 

 comprehension of the action of soil ferments will dissipate all 

 the anxiety chemists now entertain as to a gradual diminution of 

 this so essential nutrient. 



To Hellriegel, Wilfarth, Wollny, Engelmann, Winograwdski, 

 Warrington, and HerJius can be attributed the most noteworthy 

 experiments in this special line. In order to appreciate the im- 

 portance of their discoveries, I will, with your kind indulgence, 

 first give a brief historical resumS of the study of fermentation. 

 Owing to the extreme age of the use of alcoholic beverages, 

 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 Gam- 

 brinus — 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 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 expressions of "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 Valentine 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 already 

 existing in the decoction of germinated barley. In 1648 Van 

 Helmont declared fermentation the cause of all chemical action 

 and spontaneous generation, going so far as to give directions 

 for the production of mice, frogs, eels, &c. He clearly observed 

 the production of a special gas (gas vinorum) during alcoholic 

 fermentation, and stated that something from the ferment passes 

 into the fermentable substance, developing therein like a seed in 

 the soil, thereby producing fermentation. 



Willis, an English 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 ferment, the heterogeneous particles are 

 separated from each other, recombining :so as to form more 

 stable compounds, including the same principles but in different 

 proportions. Putrefaction is but a particular case of fermenta- 

 tion." This theory remained unchallenged eighty years. 



Lavoisier, by applying the new methods of organic analysis 

 he had invented, quantitatively ascertained the relations between 

 the fermented matter and the products. 



Guy Lussac considered oxygen the sole cause of fermentation, 

 putrefaction, and decay, by transmitting its motion to the fer- 

 ment and this imparted its motion to the loosely combined fer- 

 mentable mass. 



The present theories of fermentation originated with Schwann 

 and Pasteur. It took a century and a half before the experi- 

 ments which led up to Schwann's theory found a scientific 

 explanation by the work of this chemist. Leuwenhoeck had in 

 1680 already noticed that beer yeast was composed of small 

 spheroid globules. Cagniard de Latour declared ye.ist a plant 

 and the exciter of fermentation. 



Schwann's experiments were made to determine the possi- 

 bility of spontaneous generation. He found that fermentable 



NO. II 98, VOL. 46] 



fluids, when first heated in closed vessels in the presence of 

 oxygen, to the temperature of boiling water would not ferment. 

 This disproved Guy Lussac's theory that oxygen caused 

 fermentation. He next showed that purified air or oxygen 

 passed into a sterilized fermentable fluid did not induce fer- 

 mentation ; but that this set in with the introduction of ordinary 

 air. He concluded from these experiments that the air was not 

 the exciter, but simply the medium containing it, and that in the 

 floating particles of the atmosphere were organisms capable of 

 developing in the fluid ; should these be killed by heat, fer- 

 mentation would not take place. In his examination of these 

 organisms, although his methods were not absolute, his con- 

 clusions that alcoholic ferments are of a vegetable nature were 

 correct. 



Instead of general acceptance, Schwann's theory received but 

 little recognition. 



Schultze's method of first passing the air entering a sterilized 

 fermentable fluid through oil of vitriol, and that of Schroeder and 

 Dusch of filtering it through cotton can be regarded as modifica- 

 tions of Schwann's experiments. All these experiments conclu- 

 sively show that the particles in the atmosphere are the exciters 

 of fermentation but do not render them visible. 



Pasteur, spurred on by the same motive as Schwann — namely, 

 to determine the question of spontaneous generation— made a 

 simple modification of Schroeder and Dusch's experiment, by 

 substituting gun-cotton, and achieved most remarkable results. 

 The gun-cotton, containing the particles filtered from the air, 

 was dissolved in ether under the microscope, and now for the 

 first time the organisms could be thoroughly examined. 



Tyndall's well-known experiments, with the air-tight box 

 coated with glycerine, demonstrated that gravity alone can 

 purify the atmosphere so as to debar fermentation from setting in. 



Pasteur's theory is that " The chemical act of fermentation is 

 essentially a correlative phenomenon of a vital act beginning 

 and ending with it ; there is never an alcoholic fermentation 

 without there being at the same time organization, development, 

 multiplication of globules, or the continued consecutive life of 

 globules already formed. 



The following few examples will serve to show that th£ 

 slightest changes in nutrients may render them worthless as such 

 to certain ferments and available to others. Organic substances 

 showing optical rotation chiefly exist already formed in the 

 I animal or vegetable organisms, or they can be easily obtained 

 from such substances formed during vital processes. 



When these substances are made synthetically, they are 

 chemically and physically similar to the natural isomers, but 

 usually do not rotate the plane of polarized light. This leads 

 to the belief that these synthetical products consist of active and 

 inactive molecules in such proportions as to neutralize each 

 other. 



Pasteur ^ verified his hypothesis by splitting inactive racemic 

 acid into dextro-tartaric acid. Neutral ammonium racemate in 

 a solution to which the proper inorganic salts had been added 

 was fermented by means of Penicillium glaucum and beer 

 yeast. The dextro-tartaric acid was consumed and the Isevo 

 left. 



Lewkowitch- took inactive mandelate of ammonia, employing 

 either Penicillium glaucum or Bacterium termo ; in each case at 

 the end of several weeks all the fluids showed more or less 

 dextro rotation. Natural mandelic acid from amygdalin is 

 laevo rotary, therefore here, as in Pasteur's experiment, with 

 racemic acid it showed that the organisms consumed the naturally 

 produced isomer. 



Sac. ellipsoideus and split fungi consume the dextro and leave 

 the Isevo. The dextro has the same positive as the Isevo nega- 

 tive rotation. The melting points and solubility of the right 

 and left are the same, yet we see that these substances, chemically 

 and physically the same, save in their opposite rotatory powers, 

 can serve in one case as nutrients to certain organisms, and the 

 other are worthless as such. 



The Micro-organisms oj the Soil {Scuchse'). 

 These organisms, according to their actions, can be divided 

 into three groups. Those oxidizing constituents of the soil 

 those reducing or destroying the same ; and lastly those by 

 whose activity the soil is enriched. As regards the first group 

 the oxidation can take place in two ways— they can either oxi- 

 dize by assimilating the organic substances of the soil and re- 



' Cr. xlvi. 61S ; li. 398. 



3 Chem. Cent. BL, 1889, vol. ii. 169, 825. 



a B. xvi. 1503, 1569. 



