204 PHYSIOLOGY OF NUTRITION 



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

 answered in the affirmative by Pfluger, 1 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 supplied in this way. Oxida- 

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

 because the organisms in question live 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. 2 — Alcoholic fermentation consists essentially 

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

 the specific activities of organisms such as the Saccharomycetes; negligible 

 amounts of succinic acid and glycerine are also formed. This kind of fermenta- 

 tion occurs especially in the presence of yeast fungi. At first thought, it may 

 appear that the fermentation 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. Microscopic 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 perforated by wasps often exhibit large colo- 

 nies of well-nourished, budding cells. The yeasts find here a very favorable 

 substratum for growth and reproduction, and 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 micro- 

 scopical examination of the wasps or by placing them in sterilized beer-wort 

 and noting the subsequent fermentation that is set up. Wortmann performed 

 many experiments of this kind, always with the same result; after the introduc- 



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

 in den lebendigen Organismen. Pfliiger's Arch. Physiol, io: 251-367, 641-644. 1875. Pfeffer, W., 

 Das Wesen und die Bedeutung der Athmung in der Pflanze. Landw. Jahrb. 7: 805-834. 1878. Wort- 

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

 Bot. Inst. Wurzburg. 2: 500-520. 1882. 



2 Pasteur, L., Etudes sur la biere. Paris, 1876.* Mortiz, and Morris, 1891. [See note 3, p. 167-J 

 Lafar, Franz, Technische Mykologie. Ein Handbuch der Garungsphysiologie fur technische Chemiker, 

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

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

 (2 vols, in 3.) London, 1003-1010. Buchner, Buchner and Hahn, 1903. [See note 2, p. 170.] Duclaux, 

 1899-1900. [See note 2, p. 166.] Hansen, 1896. [See note 1, p. 45.] Oppenheimer, 1909. [See note 

 2, p. 166.] Wahl and Henius, American handy book of brewing, malting and auxiliary trades. [Chicago, 

 1902.] 



