402 PEACTICAL PHYSIOLOGY 



CHAPTER XLIV. 

 RESPIRATION IN THE TISSUES. 



Cell-respiration. The processes of oxidation go on in the tissue 

 cells, not in the blood which bathes them. To prove this, Pfluger 

 devised the following experiment : 



A large frog is taken and decerebrated. The anterior abdominal 

 vein is exposed, and a cannula introduced into either end. Ringer's 

 solution is injected towards the heart and the blood washed out and 

 the vascular system filled with the solution. The vein is then ligatured. 

 The animal can be put in a measure glass containing 2 over mercury. 

 After twenty-four hours the animal is withdrawn and the C0 2 absorbed 

 by potash and measured. The animal under these conditions continues 

 for twenty-four hours to put out a normal amount of C0 2 . 



If a saline solution, saturated with Ehrlich's methylene blue, be 

 injected intravenously or subcutaneously into a living animal the 

 blue is deoxygenated and rendered colourless. After the death of 

 the animal the dying tissues become blue on exposure to air. 



Other evidences of cell-respiration are these: (1) Plant-cells, egg- 

 cells, and the lower animals, which have no blood, die in the absence 

 of oxygen. In insects the finest branches of the tracheae run to the 

 single cells of the tissues ; (2) In the glow organ of Lampyris 

 Splendidula there are certain cells grouped on the ends of the tracheae, 

 which are stained black with osmic acid. These cells contain, there- 

 fore, a substance with a strong affinity for oxygen. The glow organ 

 can be sliced and the slices, examined microscopically. The points of 

 light seem to begin in the cells at the ends of the tracheae, and the 

 light goes out when oxygen is withdrawn (Max Schultze); (3) The 

 saliva contains O4 per cent. 2 . The presence of 2 in saliva can be 

 demonstrated by adding it to a solution of reduced haemoglobin, and 

 observing the appearance of the oxyhaemoglobin bands; (4) The 

 reducing substances found in the blood of an asphyxiated animal are in 

 the blood-cells. They do not occur in the plasma or lymph. Owing 

 to the reducing substances in the blood-cells oxygen disappears from 

 shed blood, and the inside of a blood clot becomes black in colour. 



