THE SEAT AND NATURE OF THE OXIDATIONS 509 



the oxidation, some other tissue may be called upon to form the final 

 product. 



The tissues possess a very pronounced avidity for oxygen. This 

 has been shown in a very convincing manner by Ehrlich. A saturated 

 solution of methylene-blue was injected into the venous bloodstream 

 of an animal. After an interval of ten minutes it was killed and its 

 organs fully exposed to the air. The tissues which exhibited at first 

 their natural color, soon assumed a decidedly blue color. It is evident, 

 therefore, that they are able to decompose the comparatively stable 

 methylene-blue into a colorless product, which on exposure to the air 

 is again oxidized into methylene-blue. It has also been noted that 

 hemoglobin-like bodies are present in the cytoplasm of the cells of the 

 worms, presumably for the purpose of effecting respiratory interchanges. 

 In addition, Lillie 1 has found that the colored products of the oxida- 

 tions, such as may be obtained in the course of indophenol and similar 

 reactions, accumulate chiefly in the vicinity of the nuclei. Some 

 light is also thrown upon this question by the fact that the tissues 

 contain large quantities of carbon dioxid and that this gas is present 

 in considerable amounts in the lymph occupying the peripheral 

 radicles of the lymphatic system. It might also be mentioned that 

 a frog may be kept alive even after its blood has been replaced by 

 physiological salt solution, by simply placing the animal in an atmos- 

 phere of pure oxygen. Inasmuch as the consumption of oxygen and 

 the production of carbon dioxid are had in this instance even in the 

 absence of the blood, these processes must actually be completed in 

 the tissues. The same result may be, obtained with excised muscles, 

 in which case the production of carbon dioxid follows a course parallel 

 to the activity and general condition of this tissue. 



In whatever form the energy of the body may be liberated, its 

 source lies in cellular combustions which in turn necessitate respiratory 

 interchanges. The nature of these microchemical and microphysical 

 processes is not clearly understood, nor has the chemist been able to 

 form a concise picture regarding the changes that occur during one of 

 the simplest possible combustions. On this account, it is quite 

 impossible to describe these processes in anything more than a very 

 general way. When the blood enters the tissues, it delivers not only a 

 definite amount of oxygen, but also certain amounts of nutritive mate- 

 rial in the form of proteins or amino acids, fats and sugars. These 

 substances are acted upon within the boundaries of the cells. Con- 

 sequently, the processes of life consist in an uninterrupted change in 

 energy which presents itself as a conversion of latent energy into work, 

 heat and electricity. It is to be noted, however, that animals are not 

 capable of sustaining themselves unless fully formed organic sub- 

 stances are placed at their disposal, and hence, the amount of energy 

 which they produce, is absolutely dependent upon their power of reduc- 

 ing these organic molecules. Plants, on the other hand, are able to 

 1 Am. Jour, of Physiol., vi, 1902, 15. 



