RESPIRATION 101 



chemical relations of the tissues to the atmosphere must be briefly dis- 

 cussed, and in. a most general way the biochemistry of oxidation. 



Oxidation is a process probably more nearly universal on the planet 

 Earth than any other chemical reaction with which we are familiar. 

 One-half of the crust of the world is oxygen, as is more than one-fifth of 

 the atmosphere and about four-fifths of all the water. Oxygen is the 

 source of all "combustion," and furnishes to organisms one of their 

 sources of energy. Not only all animals but also all plants (a few indi- 

 rectly) are dependent on oxygen for their living. Oxygen combines 

 with all " elements" so far isolated (except fluorine). This fact partly 

 accounts for its very wide distribution in nature. The protein particle 

 contains oxygen, and so does the carbohydrate molecule, the molecule 

 of fat, and that of albuminoid. Moreover, each of these molecules 

 contains carbon, with a strong affinity for oxygen, and this, when satis- 

 fied, gives rise to carbon dioxide. Later on, in the chapter on Nutrition, 

 we shall study somewhat more in detail the metabolic processes of the 

 body. The important fact now is that the atmosphere and the food con- 

 tain both oxygen and carbon, and that these are prominent also in the 

 animal tissues. Life in its basis is but a physiological succession of 

 anabolism (building-up), and of katabolism (tearing-down), the vital 

 animal energies being made kinetic, apparent, useful, in the latter or 

 katabolic process. Even tissues excised from the body of an animal 

 respire, that is, absorb oxygen and give off carbon dioxide. Thus, Bert 

 obtained from the tissues of a dog recently killed an interchange of 

 the two gases in twenty-four hours as follows : 



RESPIRATION OF EXCISED TISSUES. 

 Cubic centimeters of gas per 100 grams of tissue. 



Tissue. Oxygen absorbed. ^^^^ 



Muscle 50.8 56.8 



Brain 45.8 42.8 



Kidney 37.0 15.6 



Spleen . . 27.3 15.4 



Testis 18.3 27.5 



Broken bone and marrow . ... 17.2 8.1 



These quantities are interesting because they prove, among other 

 things, that respiration is inherent in living tissues. A molecule of proto- 

 plasm in the dying muscle from a dog respires quite as does a molecule 

 of the protoplasm of an ameba or of a human spermatozoon. Nothing 

 further is needed to prove that the animal combustion which requires 

 the oxygen and produces the carbon-dioxide takes place in the tissues 

 themselves, and not for the most part in the circulating blood, as was 

 formerly supposed. The blood is a tissue and has its share of direct 

 oxidation, but most of the oxygen absorbed into the body goes as directly 

 into the protoplasmic cells of the tissues as the complexity of the struc- 

 tural conditions will allow. 



