230 PHYSIOLOGY OF NUTRITION 



bryos, which were much richer in nuclein substances, was thus seventeen times 

 as vigorous as that of the entire seeds. 



Respiration in seed-plants occurs, in general, by the destruction of carbohy- 

 drates. Its dependence upon proteins is due (1) to the fact that carbohydrates 

 may be formed, under certain conditions, from proteins, and (2) to the fact that 

 respiratory enzymes are formed by the protoplasm; on the amount of protoplasm 

 depends the amount of these enzymes, and, consequently, the rate of respiratory 

 activity. 



§12. Special Cases of Respiration in Lower Plants. — In many lower forms 

 of plant life carbohydrates are not the substances that are decomposed in respira- 

 tion. Among these forms occur not only various types of fermentation, as has 

 been pointed out, but also various types of aerobic respiration. The respiration 

 process in acetic-acid bacteria, for example, is just an oxidation of ethyl alcohol 

 to acetic acid, according to the following equation: 



Ethyl Alcohol Oxygen Acetic Acid Water 



CH 3 CH 2 OH + 2 = CHaCOOH + H 2 0. 

 This process is really not a fermentation at all, in the restricted sense of this 

 term; it is to be regarded as a special kind of aerobic respiration. The true fer- 

 mentations (anaerobic respiration) are characterized by the decomposition of 

 complex compounds into simpler ones, while oxidations are characteristic of 

 aerobic respiration. As long as alcohol is present, the end product of the respira- 

 tion of these organisms is acetic acid, but as soon as the supply of alcohol has 

 been completely consumed they begin to oxidize acetic acid into carbon dioxide 

 and water. 



Pasteur was the first to recognize acetic acid fermentation as a vital process, 

 and he thought that the bacteria controlling it were of the single species, My- 

 coderma aceti. Hansen 1 showed later that the bacterial membranes (mother) 

 arising during this process consist mainly of three different species of bacteria, 

 Bacterium aceti, Bacterium pasteurianum and Bacterium kuetzingianum. These 

 three forms are briefly described below. 



Bacterium aceti, when grown on beer at room temperature, forms (in twenty- 

 four hours) a smooth slimy skin, which consists of chains of rod-like cells (Fig. 94) . 

 These cells are colored yellow by iodine. With a temperature of from 40 to 

 45°C. the rod-like cells form long, thin filaments. 



Bacterium pasteurianum, grown on beer, forms a dry superficial skin, which 

 is usually wrinkled. This consists also of chains of rod-like cells (Fig. 95) , but the 

 latter are larger than in the form just described. The slimy layer surrounding 

 the cells of a newly-formed skin is colored blue by iodine. 



Bacterium kuetzingianum forms, on beer at 34°C, a dry surface skin which 

 grows upward at the edges, on the walls of the culture-vessel. The skin con- 

 sists of rod-like cells but these do not occur in rows or chains but are generally 

 single or joined in pairs. The slime about the cells is colored blue by iodine, as 

 in the last form. 



1 Hansen, Emil Christian, Rechcrches sur les bacteries acetifiantes. Compt. rend. trav. Lab. Carlsberg, 

 Kjobenhavn 3'": 182-216. 1894. (Rev. by Fr. Lahar in Bot. Zeitg. 52": 337-342. 1894-! 



