ANIMAL OXIDATIONS. 441 



The fact that the oxygen in the condition in which it is given up to the 

 tissues is not capable of consuming the unchanged nutriment, enables the 

 cell to adjust the metabolism to its requirements. Above all, this fact 

 enables the cell to utilize a certain particular material for definite functions 

 when it so desires. We should also not forget that we know altogether too 

 little concerning the relations of the separate organs to one another, and 

 of the different kinds of cells in one and the same organ, to be able to 

 judge whether under all conditions, the combustion of the fuel is entirely 

 effected by the cell that begins the work, or whether one cell merely 

 carries the oxidation to a certain stage, and another cell carries the com- 

 bustion farther, until finally the material is completely oxidized. Such 

 an assumption seems extremely probable from the observations of Bohr 

 and Henriques, 1 who found that extensive oxidations take place in the 

 lungs. Oxygen is consumed there and carbon dioxide evolved to an extent 

 sufficient to lead one to presume that incompletely oxidized, metabolic 

 products reach the lungs together with the blood, and that the combustion 

 is completed by the lungs. On the other hand, according to the assump- 

 tion that the respiratory exchange takes place as a sort of secretion process, 

 it is probable that the lungs have a certain amount of work to do which 

 requires the expenditure of energy, so that this supply of fuel is necessary 

 for its function. Bohr and Henriques found that about one-third of the 

 total metabolism taking place in the body was effected in the lungs. The 

 separate observations varied from to 66 per cent. 2 



We must emphasize the fact at the start that we are not yet able to give 

 a perfectly clear explanation as to the nature of animal oxidation processes. 

 At present, we recognize merely the initial products, food and oxygen, and 

 the final products of the combustion. We are therefore forced to rely 

 upon assumptions. In fact, the great number of hypotheses which have 

 been brought forward, show clearly upon what an insecure foundation they 

 all rest. Here we will only attempt to mention only the more important 

 theories, and emphasize only those which rest, to some extent, upon 

 experimental observations. 



The question to interest us first of all is this: Is the oxygen changed 

 in form so that it attacks the nutriment more readily? The formation 

 of ozone has been suggested. We know that ozone is a stronger oxidizing 

 agent than ordinary oxygen, and oxidizes compounds which are not 

 affected by the latter. Schonbein 3 carried his studies on ozone to the 

 phenomena of cell life. He attributed numerous oxidations taking 

 place in the plant organism to the primary formation of ozone. The plant 

 tissues, he assumed, contain some substance which possesses the power of 



1 Arch, de Physiol. 1897, 590. See Lecture XVIII, p. 432. 



2 These high figures have not been generally accepted. Translator. 



3 Poggendorff's Annalen, 65, 171 (1845). 



