RESPIRATION 611 



Higher Fungi. Kostytschev (1910) showed that mushrooms in absence of 

 oxygen do not form alcohol. In their press juice an interesting phenomenon was 

 observed. Carbon dioxide is formed and can be driven off by boiling. It arises 

 only in small part from carbonates and chiefly from some substance which splits 

 off carbon dioxide by hydrolysis. The carbamino-acids of Siegfried were excluded 

 by the observation that the phenomenon could be observed in the absence of 

 proteins or amino-acids. The substance in question seems to be some intermediate 

 stage of oxidation, formed by previous exposure to oxygen. It was found that 

 mannite disappears, if added to the press juice, without giving off carbon dioxide 

 until the solution is heated, and it is thought probable that this substance is the 

 source of the interesting compound in question. 



Higher Plants. Considerable evidence exists that, in absence of oxygen, higher 

 plants attack sugar as yeast does, forming alcohol and carbon dioxide. Further 

 details may be found in the essay by Lesser (1909). 



In Animals. The behaviour of frog's muscle in absence of oxygen has.been 

 described above (page 444). We saw that there is no evidence of any chemical 

 process going on in rest, apart from the action of micro-organisms ; -when 

 stimulated, the substance of high potential energy content gives off lactic acid and, 

 when the store of the substance is exhausted, the muscle ceases to contract. 

 When the muscle is placed in oxygen, lactic acid is replaced in the system by aid 

 of an oxidation process, which forms carbon dioxide from some other substance. 

 In a certain sense, we may say that lactic acid is the product of anaerobic change 

 in muscle, carbon dioxide that of aerobic change. But it must not be forgotten 

 that they do not arise from the same source. 



Intestinal Worms. These are the only multicellular animals known which 

 normally exist in absence of oxygen. Although they have no need to produce heat, 

 they require energy for other purposes, muscular movement, growth, and so on. 

 They are, therefore, very instructive for investigation. The most recent work 

 is that of Weinland (1901-1906). These worms were found to contain large 

 quantities of glycogen, which was consumed in starvation, giving as products, in 

 absence of oxygen, carbon dioxide as the only gas. In -the liquid around the 

 animals, valerianic acid was found, in amount corresponding to 0'3 g. per 100 g. 

 of Ascaris in twenty-four hours, together with a nitrogenous substance containing 

 0'015 g. nitrogen for the same time and weight of animals. The carbon dioxide 

 was 0'4 g. The process is represented as follows : 



4C 6 H 12 6 = 9C0 2 + 3C 5 H 10 2 + 9H 2 . 



The hydrogen is supposed to be used up at once for reduction processes. If this be 

 so, we have a true fermentation process. 



The Leech. Putter (1907) has investigated the metabolism of the leech, which 

 can live ten days without oxygen. He states that hydrogen is formed in these 

 conditions. When first placed in water deprived of oxygen, the carbon dioxide 

 production goes up considerably for a time, but afterwards falls again. 



Energetics of Anaerobiosis. It appears from the preceding paragraphs that a 

 larger amount of carbon dioxide has to be given off by a fermentation process than 

 by an oxidation in order to give the amount of energy required by an organism. 

 Indeed, Warburg (1914, p. 262) calculates that the same quantity of glucose when 

 decomposed to alcohol and carbon dioxide only gives 3 to 5 per cent, of the energy 

 which it gives when completely burnt to carbon dioxide and water. But the 

 general conclusion seems to be justified that the cell mechanisms are such as to 

 be able to use chemical energy whether it comes from oxidation or otherwise, 

 and that they are independent of the particular chemical reaction which affords it. 



It would naturally be supposed that the anaerobic changes of a food-stuff 

 would pass through the same stages as those which the same substance undergoes 

 in the presence of oxygen, but stop short. Thus, glucose might be thought in 

 all cases to pass through the stages of alcohol and carbon dioxide, but that, in 

 the presence of oxygen, the alcohol is further oxidised to carbon dioxide and 

 water. This, in fact, was the view suggested by Pfeffer (1881-1885, p. 664), and 

 it appears to be the case in some instances. Yeast, however, does not ferment 



