204 THE BLOOD. 



SECTION IV. GASES OF THE BLOOD. 



1. The gases of the blood are ox3'gen, carbonic acid and 

 nitrogen. The knowledge we possess of the conditions under 

 which they are contained in the blood, and of the relative 

 quantities of each, is founded entireh* on the researches of 

 Liulwig and his pupils, published during the first } r ear of the 

 last decade. 



As regards oxygen, a correct method (that of displacement 

 by carbonic oxide) had already been employed by Claude 

 Bernard ; but, as regards carbonic acid, the methods previous- 

 ly used were imperfect and the results erroneous. 



2. In round numbers, one hundred volumes of arterial blood 

 deliver to the Torricellian vacuum about twenty volumes of 

 oxygen (estimated at 760 millimetres pressure and temper- 

 ature) venous blood about twelve volumes. Of the quantity 

 of oxygen so extracted, by far the greatest part is in combina- 

 tion with haemoglobin in other words, in the concrete state. 

 The proportion of free oxygen in blood is so small that oxygen 

 is absorbed from any atmosphere containing it in which its 

 tension is greater than from twenty to twenty-live millimetres 

 in other words, from any space in which it exists in a pro- 

 portion greater than about one-eighth of the proportion in 

 which it exists in the atmosphere. Consequently, in subject- 

 ing blood to the air-pump, no oxygen is given off till the press- 

 ure sinks to about 125 millimetres (i. e., about a sixth of an 

 atmosphere) ; whereas, in the case of other liquids (e. <?., 

 water), oxygen, with the other contained gases, begins to be 

 disengaged, pari ;w,s-s?/, with the reduction of pressure, in a 

 quantity doterminable according to Dalton's law. These facts 

 are expressed by snying (1) that the absorption of oxygen by 

 the blood is independent of Dalton's law, and (2) that the ten- 

 sion of oxygen in the blood is from twenty to twenty-five 

 millimetres of mercury. 



3. When blood is subjected to the Torricellian vacuum, the 

 disengagement of oxygen is complete. The blood is converted 

 into froth, and rapidly assumes a dark color. This appear- 

 ance is due partly to the discharge of the coloring matter from 

 the corpuscles, partly to the complete reduction of the haemo- 

 globin which accompanies the extraction from the liquor san- 

 (juimxi of its free oxygen. 



4. When blood is subjected to an atmosphere which con- 

 tains no oxygen, the result, so far as relates to the extraction 

 of oxygen, is the same as if it were exposed to the vacuum. 

 This is particularly the case if the gas employed be one which 

 has the power of combining with haemoglobin. The gas which 

 pre-eminently enjoys this faculty is carbonic oxide. When 

 blood is subjected to an atmosphere of this gas, the oxygen it 



