320 PULMONARY MUCOUS TISSUE. 



with the air of the lungs, by yielding up to it a portion of its 

 heat. 



This fact was long disputed ; first, because direct experi- 

 ment on the subject seemed to contradict it : two thermom- 

 eters, placed, one in the left heart, and the other in the right, 

 seemed to show an increase of heat in the former cavity, and 

 a consequent heating of the blood in its passage towards the 

 lung : more careful examination has, however, led to an entirely 

 opposite conclusion (Cl. Bernard), and shown that, in former 

 experiments, allowance had not been made for the inequality 

 of thickness in the coats of the two ventricles, occasioning 

 a greater loss of heat in the right ventricle (the coats of 

 which are thin), than in the left (of which the coats are 

 thick). 1 In the second place, the increased temperature of 

 the arterialized blood was looked upon as the necessary con- 

 sequence of the hypothesis that actual combustion takes place 

 in the lungs, and that it is here that the oxygen absorbed 

 during inspiration is employed to consume the carbon and 

 produce the carbonic acid exhaled in expiration. 



It is now, however, proved that the production of carbonic 

 acid in the blood is not limited to the pulmonary surf-ice, but 

 occurs in the whole organism, throughout the current of the 

 circulation, and, more particularly, in the capillary network: 

 carbonic acid is, indeed, found everywhere in the venous 



1 Following experiments made recently, Heidenhain and Kbrner 

 have sought to prove that the difference in temperature between 

 the blood of the left heart and that of the right is not caused by 

 the cooling of the blood in its passage into the lungs. They main- 

 tain that the blood is neither cooled nor heated in passing through 

 the lungs, but that the higher temperature of the right ventricle 

 is caused by its being situated more immediately in the phrenic 

 centre, and, consequently, being in contact with the organs con- 

 tained in the abdominal cavity (the liver, stomach, and intestines), 

 which have all a higher temperature than that of the organs of the 

 thorax. Cl. Bernard, however, opposes this theory by instancing 

 those cases of ectopia (or displacement) of the heart, in which the 

 heart from its transposition is not in contact either with the dia- 

 phragm or with the abdominal viscera, and yet contains warmer 

 blood in the right ventricle than in the left. On the other hand, 

 the heart of a dog, surrounded by its pericardium, and is in no 

 way united to the diaphragm, floats in the chest, if we may be 

 allowed the expression; by changing the position of this animal, 

 the relation of the diaphragm to the ventricle is modified, without, 

 however, changing the relation between the temperature of the 

 blood of the two ventricles. (Cl. Bernard, Cours de 1872.) 



