FERMENTATION AND RESPIRATION l8l 



ship between the two, as they occur in organisms; this question was first 

 answered in the affirmative by Pfliiger/ whose conclusions in this regard are now 

 generally accepted. In living animals and plants various kinds of organic de- 

 compositions are always going on, under the influence of specific intracellular 

 enzymes. In some cases, as in the microorganisms that produce various kinds 

 of fermentation, the entire energy requirement is supphed in this way. Oxida- 

 tion of the decomposition products thus formed may fail to occur here, either 

 because the organisms in question Uve in the absence of oxygen or because, 

 they lack the necessary oxidation enzymes. It may also occur that the fermen- 

 tation products diffuse out of the cells before oxidation can occur, especially in 

 the case of organisms that develop in a liquid medium. Most plants, however, 

 absorb oxygen by means of their oxidizing enzymes, thus allowing the complete 

 oxidation (to water and carbon dioxide) of the decomposition products that 

 arise from the breaking down of complex nutrient materials. This constitutes 

 aerobic or normal respiration. If ordinary plants are deprived of free oxygen, 

 then their respiratory processes become restricted to those of fermentation, 

 which is thus seen to be a fundamental process characteristic of all plants. 



§2. Alcoholic Fermentation.^ — Alcoholic fermentation consists essentially 

 in the spUtting of various sugars into ethyl alcohol and carbon dioxide through 

 the specific activities of the Saccharomycetes ; negligible amounts of succinic 

 acid and glycerine are also formedf This kind of fermentation occurs only in 

 the presence of yeast fungi. At first thought it may appear that the fermenta- 

 tion of grape juice is an exception to this statement, since yeast is not added to 

 the juice, but Pasteur showed that yeast fungi are also effective here. Micro- 

 scopic examination demonstrates the presence of various kinds of yeasts upon 

 the outer surface of the fruit of the grape, and when the berries are pressed these 

 pass into the juice, where they multiply and give rise to alcoholic fermentation. 

 Yeast cells are not numerous on uninjured grapes, but berries that have been per- 

 forated by wasps often exhibit large colonies of well-nourished, budding cells. 

 The yeasts find here a very favorable substratum for growth and reproduction 

 arid the cells are carried from one bunch to another by the wasps. All of these 

 insects are found to be carriers of yeast cells during the grape season, as may be 

 shown either by direct microscopical examination of the wasps or by placing 

 them in sterilized beer-wort and noting the subsequent fermentation that is 

 setup. Wortmann performed many experiments of this kind, always with 

 the same result; after the introduction of the wasp the medium soon began to 



» Pflfiger, E., F. W., Beitrage zur Lehre von der Respiration. I. Ueber die physiologische Verbrennung 

 in den lebendigen Organismen. Pflflger's Arch. Physiol. lo: 251-367, 641-644. 187S. Pfeffer, W., 

 Das Wesen und die Bedeutung der Athmung in der Pilanze. Landw. Jahrb. 7 : 80s- 834, 1878. Wort- 

 mann, Julius, Ueber die Beziehungen der intramolecularen zur normalen Athmung der Pflanzen. Arbeit, 

 Bot. Inst. Wurzburg. 2 : S00-S20. 1882. 



"Pasteur, L., Etudes sur la biSre. Paris, 1876.* Moritz, and Morris, 1891. [See note 3, p. 149-1 

 Lafar, Pranz, Technische Mykologie. Ein Handbuch der Garungsphysiologie fur technische Chemilser, 

 nahrungsmittelchemiker usw. Jena, 1897-1907. Idem, Technical Mycology; the utilization of micro- 

 Srganisms in the arts and manufactures. A practical handbook, etc. Translated by Charles T. C. Salter. 

 (2 vols, in 3.) London, 1903-1910. Buchner, Buchner and Hahn, 1903. [See note 2, p. 152.] Duclauz, 

 1899-1900. (See note 2, p. 148. 1 [Hansen, iSg6. [See note i, p. 42-1 Oppenheimer, 1909. [S^ 

 note 2, p. 148.] Wahl and Henius, American handy book of brewing, malting and auxiliary trades. 

 Chicago, 1902.] 



