90 The Functions of the Blood. 



of time. Hence the process indicated a delicate and certain 

 test for use in cases of suspected poisoning by carbonic oxide. 

 I myself, in ignorance of Hoppe-Seyler's experiments, made 

 the same observations. I have by me now a sealed tube, which 

 has for more than a year contained a solution of blood through 

 which carbonic oxide had been passed. The spectrum has not 

 altered in the slightest degree.* 



To return from this digression, it is clear that we are now 

 acquainted with the mode in which oxidation is effected in the 

 body, as far as the earlier stages go. Oxygen is absorbed in 

 the lungs, combines with the cruorine, and is afterwards given 

 out again. But at this point we are compelled to pause to 

 consider two more complex and exceedingly important questions. 

 These are, firstly, What is oxidized ? and, secondly, Where i 

 is the oxidation effected? Liebig, as everybody knows, divided 

 the substances oxidized in the body into two great classes, 

 corresponding with the chief constituents of food. These were 

 the non-nitrogenous, or " respiratory" elements, and the nitro- 

 genous, albuminous, or " plastic " elements. The former em- 

 braced fat, sugar, starch, etc., and all its members were 

 supposed by him to be oxidized in the blood, and to evolve no 

 force but heat as the result of their combustion. The latter 

 consisted of the organized tissues, and in particular the mus- 

 cular tissue, the oxidation of which chiefly resulted in the 

 production of mechanical work. It is an obvious corollary 

 from this hypothesis, that the oxidation of a solid tissue must 

 be effected in the tissue itself, outside the walls of the capil- 

 laries, and we are therefore compelled to believe in two distinct 

 modes of oxidation. Substances in the blood are in direct 

 contact with the corpuscles, and may therefore be supposed to 

 unite directly with the oxygen of the scarlet cruorine; whereas, 

 for the direct oxidation of a tissue, it is necessary to assume 

 that some of the oxygen leaves the corpuscles, traverses the 

 walls of the blood-vessels, and arrives at the comparatively 

 distant fibres in a state of solution, but in an uncombined con- 

 dition. In its extreme form, Liebig's hypothesis has long 

 been known to be untenable, for ifc cannot be doubted that 

 nitrogenous substances, as well as non-nitrogenous ones, are 

 oxidized in the blood, and contribute to the animal heat ; and 



* I believe reduced cruorine to be the most delicate, as it certainly is one of 

 the simplest, qualitative tests for oxygen known. If a weak solution of blood is 

 inverted in a test tube over mercury, it reduces itself in a day or two, and a small 

 prism will then show (he one-line spectrum. The minutest trace of oxygen will 

 now restore the original spectrum ; a single drop of distilled water will often 

 contain enough. I obtained incidentally in the above experiments a confirmation 

 of the previously known fact, that carbonic oxide is disengaged during the ab- 

 sorption of oxygen by potassic pyrogullute. Air from which the oxygen had been 

 removed by this re-agent, when added to reduced cruorine, caused the latter to 

 give a two-line spectrum, which lasted for weeks. 



