INTERNAL RESPIRATION OR TISSUE-RESPIRATION'. 243 



excrete a large amount of carbon dioxid and consume much oxygen. The inter- 

 change of gases in tissues is increased during their activity. The secreting salivary 

 glands, kidneys, and pancreas are no exception to this rule; for although, in the 

 secreting state, bright red blood flows away from them through the dilated vessels, 

 still this apparently relative diminution in the carbon dioxid of the venous blood 

 is more than compensated for by its absolute increase through the marked increase 

 in volume of the blood passing through these organs. 



Active reduction-processes take place in most tissues. If coloring-matters, 

 such as alizarin-blue, indophenol-blue, or methylene-blue, be introduced into the 

 blood of animals, the tissues will soon be stained. Those organs that have an 

 especially strong affinity for oxygen (such as the liver, the cortex of the kidneys, 

 and the lungs), abstract oxygen from these coloring-matters, and change them into 

 colorless reduction-products. The pancreas and the submaxillary gland have 

 almost no reducing power. 



2. The blood itself, like all of the tissues, is a seat for the consumption 

 of oxygen and the formation of carbon dioxid. This is proved by the fact 

 that blood removed from the body quickly becomes poorer in oxygen 

 and richer in carbon dioxid; further, by the circumstance that in the 

 oxygen-free blood of asphyxiated persons and in the blood-corpuscles 

 there are always found small quantities of reducing agents, which become 

 oxidized on the addition of oxygen. At all events, this gaseous inter- 

 change is but slight as compared with that occurring in all the other 

 tissues. It is incontestable that the walls of the blood-vessels, by 

 means of their contained muscular fibers, also consume oxygen and 

 produce carbon dioxid, although this process is so insignificant that the 

 blood undergoes no visible change in color throughout its arterial course. 



C. Ludwig and his pupils have proved by specially adapted experiments that 

 transformation into carbon dioxid can actually occur within the blood. If sodium 

 lactate, which is easily oxidized, be mixed with blood, and this mixture be sent 

 through the blood-vessels of a recently excised organ that is still alive (such as 

 the kidney or the lung) , a more abundant consumption of oxygen and formation 

 of carbon dioxid will occur in this mixed blood than would occur in pure blood 

 similarly transfused. 



3. It may in advance be concluded as probable that the living 

 pulmonary tissue also consumes oxygen and generates carbon dioxid. 

 By passing arterial blood through lungs that have been deprived of air, 

 C. Ludwig and Miiller succeeded in demonstrating a diminution in the 

 oxygen and an increase in the carbon dioxid. Bohr and Henriques con- 

 cluded further from their experiments, in which they restricted to a 

 considerable degree the circulation of blood through the bodily tissues, 

 and found no significant diminution in the excretion of carbon dioxid 

 from the lungs, that the pulmonary tissue is not limited to a mere 

 excretion and absorption of gases, but that it besides possesses the prop- 

 erty of forming carbon dioxid from substances that are derived from 

 the other tissues. In like manner they assumed that oxygen is actively 

 taken up by the lungs; that is, the lungs secrete carbon dioxid and 

 absorb oxygen like a secreting gland. 



As the total amount of carbon dioxid and oxygen in the whole 

 volume of blood at any one time is only about 4 grams, while the amount 

 of carbon dioxid excreted daily is 900 grams, and the amount of oxygen 

 absorbed is 774 grams, it is evident that the interchange of gases pro- 

 ceeds with great rapidity, that the absorbed oxygen must be consumed 

 and the carbon dioxid formed must be excreted quickly. 



As a result of an increased introduction of acids into the body there is a 

 diminution in the consumption of oxygen (and in the production of heat), which 

 in a high degree may give rise to an internal asphyxia of the tissues. 



