288 PULMONARY MUCOUS TISSl 



the cone contains air nearly resembling atmospheric air : the 

 air in the middle zones is less pure than this, but less degen- 

 erated than the first, containing only T *o of carbonic acid. 1 

 Thus it rarely happens that the respiratory blood network 

 comes in direct contact with ordinary atmospheric air. 



Grehant, replacing atmospheric air by hydrogen, succeeded 

 in determining how many respiratory movements are neces- 

 sary for the gas and the former contents of the lung to be so 

 mingled as to become homogeneous. These experiments 

 show that at least four or five successive respiratory move- 

 ments are required to renew the gas contained in the pul- 

 monary cone. By giving a certain quantity of hydrogen to 

 a person to breathe, and then, in a series of experiments, 

 analyzing the gas from the first, second, and third expiration, 

 etc., Grehant found that it is generally only after five inspir- 

 ations and expirations, made in a receiver full of hydrogen, 

 that this gas is uniformly spread throughout the lung. These 

 experiments are extremely exact, for the blood scarcely 

 absorbs any hydrogen (the difference made by absorption 

 being scarcely ^ ). 



The introduction of air into the respiratory cone and its 

 expulsion take place by means of the respiratory move- 

 ments of inhalation and exhalation. 



A. Inhalation. 



The movement, by means of which inhalation takes place, 

 consists in increasing the distance between the base and the 



shall see later, this gas cannot be exhaled, the lung being never 

 entirely empty : he analyzed those layers only which precede the 

 one in question, and we may therefore infer that the proportion of 

 carbonic acid in this latter must equal or even exceed 8 or 9 per cent. 

 Grehant's experiment is as follows : 500 cubic cent, of hydrogen 

 are inhaled, and then immediately two exhalations are made, the 

 second into a small india-rubber bag, furnished with a stop-cock, 

 from which the air is entirely excluded by compression and by the 

 presence of a small quantity of hydrogen, previously introduced. 

 If the gas collected iu this bag be analyzed, as the hydrogen is 

 replaced by common air, it is found to contain 7.5 per cent of car- 

 bonic acid, 13.5 of oxygen, and 78.6 of nitrogen. 



1 Becher and Holmgren, by sounding the lung with a probe, 

 extracted the air from the bronchi (middle zones of the pulmonary 

 cone) , and found it to contain carbonic acid in the proportion of 

 2.3 per cent. (See T. Strauss, " Des Travaux Recents sur les Gaz 

 du Sang et les Echanges Respiratoires." (Archiv. Gener. de 

 Medecine, 1873.) 



