CHAPTER XXXIX 



RESPIRATION 



Vocabulary 



Lymph, the liquid part of the blood, in contact with cells. 



Pleural membranes, a double membrane covering lungs. 



Intermittent, not continuous. 



Depression, lowering. 



Haemoglobin, the red, oxygen-carrying part of the blood. 



Respiration is the process by which each cell of the body takes 

 in oxygen and gives off carbon dioxide and water. It is tissue oxi- 

 dation. The breathing movements, which renew the air in the lungs, 

 and the circulation of blood, which is the means of transportation 

 between lungs and tissues, are merely helps in the real process of 

 respiration which goes on in every cell of the body. 



Need of Circulation. These breathing and circulatory processes 

 are required because of the distance of the living cells from the 

 outer air and merely serve to keep the lymph supplied with oxygen 

 and freed from waste. It is between the lymph and each living cell, 

 that respiration actually goes on. 



The organs generally associated with respiration, such as the 

 lungs, trachea, etc., are really concerned with supplying oxygen to 

 the blood and removing wastes. No more actual respiration (cell 

 oxidation) goes on in the lungs, than in any other active tissue, 

 but it is in the lungs that the haemoglobin of the blood receives its 

 load of oxygen and unloads its carbon dioxide and water. 



Development of Respiration. Respiration in the protozoa took 

 place by direct contact of each cell with the air dissolved in the 

 water. In the worms the blood circulated in the skin and obtained 

 its oxygen direct from the air. In still higher forms, like crayfish 

 or fish, gills were developed with great extent of surface to absorb 



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