2IO PHYSIOLOGY OF NUTRITION 



When lactic acid is fermented instead of sugar the reaction becomes the 

 following: 



Hydro- Carbon 

 Lctica acid gen dioxide Butyric acid 



2 C 3 H 6 3 = 2 H 2 + 2 C0 2 + C 4 H 8 2 . 



To obtain butyric acid fermentation a mixture is prepared containing 2 1. 

 of water, 100 g. of potato starch (or dextrin), 1 g. of ammonium chloride and 

 other nutrient salts, and 50 g. of chalk, and this is allowed to stand at 4o°C. 



Numerous bacteria are known that cause different kinds of fermentation, 

 but an account of each separate process is not here possible. It should be men- 

 tioned, however, that these various bacteria produce numerous and diverse 

 chemical reactions, far surpassing the well-known chemical reagents in sensi- 

 tiveness and specificity. 1 



§4. Plant Respiration. 2 — Ingen-Housz (1779) was the first to demonstrate 

 that living plants respire. In repeating the experiments of Priestley upon the im- 

 provement of air by plants, Ingen-Housz showed that this alteration of the air 

 is accomplished only by the green parts of plants and that it occurs only in sun- 

 light; the non-green parts of plants are like animals, as far as their effect upon 

 the air is concerned, and unilluminated green plant parts also act in the same 

 way, to "poison" the air. (See p. 2.) This poisoning of the air is due to the 

 elimination of carbon dioxide and is the result of respiration. The first exact 

 experimentation upon plant respiration was carried out by Saussure in 1804. 



The influence of external conditions upon the respiratory activity of plants 

 has received the attention of many investigators. The effect of temperature 

 has been studied with unusual care, 3 thermostats of various kinds being used to 

 keep the temperature constant during the period of an experiment. The rate 

 of gaseous exchange is nearly proportional to the temperature, for medium tem- 

 peratures, but a maximum rate is reached at about 4o°C. and further rise in 

 temperature is without influence upon this rate, which remains constant until 

 death supervenes. The value of the respiratory ratio (the amount of carbon 

 dioxide given off divided by the amount of oxygen absorbed in a unit of time, 



CO 



~?^~ ) reaches a minimum at about io° or i5°C, and increases with higher as 

 U2 



well as with lower temperatures, the increase being more rapid in the first case. 

 This is illustrated by the following table of experimental results, taken from the 

 work of Purievich. 4 



1 Omeliansky, W., De la m6thode bact6riologique dans les recherches de chimie. Arch. sci. biol. 

 St. P6tersbourg 12: 224-247. 1907. 



2 Palladin, 1909. [See note 2, p. 204.] Czapek, Friedrich, Die Atmung der Pflanzen, Ergeb. Physiol. 

 9: 587-613. 1910. Nicolas, G., Recherches sur la respiration des organes vegdtatifs des plantes vascu- 

 laires. Ann. sci. nat. Bot. IX, 10: 1-113. 1909. Reinitzer, Fr., Ueber Atmung der Pflanzen. (Antritts- 

 rede.) 17 p. Graz, 1909. Rev. in: Bot. Centralbl. 115: 52. 1910. 



3 Wolkoff, A. v., and Mayer, Adolf, Beitrage zur Lehre iiber die Athmung der Pflanzen. Landw. Jahrb. 

 3: 481-527. 1874. Bonnier, Gaston, and Mangin, Louis, Recherches sur la respiration et la transpira- 

 tion des champignons. Ann. sci. nat. Bot. VI 17: 210-305. 1884. Kuijper, J., Ueber den Einfluss 

 der Temperatur auf die Atmung der hoheren Pflanzen. Recueil trav. bot. Neerland. 7 131-240. 1910. 



4 Puriewitsch, 1893. [See note 2, p. 188.] 



