312 THE BLOOD. 



they are present as chlorides, phosphates, carbonates, and to a slight 

 extent also as fluorides. Some of these occur in the blood as such, 

 while others form more or less intimate combinations with the albu- 

 mins. The iron largely occurs as an integral constituent of the 

 haemoglobin molecule, of which it forms from 0.39 to 0.47 per cent. 

 Traces are also present in certain leucocytes, and notably those of 

 the oxyphilic variety. In the plasma itself it is at times met 

 with in innnitesimally small amounts, and is then referable to the 

 destruction of leucocytes. 



In addition to these constituents of the normal blood, we further 

 meet with certain gases, viz., oxygen, carbon dioxide, and nitrogen. 

 Of these, oxygen and carbon dioxide occur partly in solution and 

 partly in combination with hemoglobin, while nitrogen is found 

 only in solution. The carbon dioxide, moreover, is in part present 

 as a soluble bicarbonate, and to a certain extent also in combina- 

 tion with the albumins of the plasma. These gases may be ex- 

 tracted from the blood in their entirety by exposure to a vacuum. As 

 the nitrogen is simply held in solution, its volume is constant, and 

 corresponds to 2 per cent, by volume no matter whether the blood 

 is obtained from an artery or a vein. The relative amount of oxy- 

 gen and carbon dioxide, on the other hand, is subject to great varia- 

 tions. From the arterial blood of dogs it is thus possible to obtain 

 21 per cent, of oxygen by volume, and 38 per cent, of carbon di- 

 oxide, while venous blood contains as much as 46 percent, of carbon 

 dioxide and only 12 per cent, of oxygen. 



As these gases can be obtained by exposure to a vacuum, it follows 

 that their combination with oxyhsemoglobin cannot be very strong ; 

 it is surprising, however, to note that in this manner not only that 

 portion of the carbon dioxide is obtained which is in combination 

 with albuminous material, but also the carbon dioxide of the car- 

 bonates. This phenomenon is owing to the fact that in conse- 

 quence of the vacuum the red corpuscles are broken down, and 

 that the haemoglobin w r hich is thus set free is then capable of exer- 

 cising its acid properties, and causes decomposition of the salts. 



The Plasma. 



Tn order to obtain blood-plasma it is necessary to prevent coagu- 

 lation of the blood. This may be accomplished in various ways. 

 It has thus been found that following the intravenous injection of 

 certain albumoses (peptones), or of an infusion of the mouth parts 

 of the officinal leech, as also after ligation of the bloodvessels of 

 the liver and intestines, the blood remains liquid after being 

 shed. On allowing it to stand at a low temperature the blo< Mi- 

 corpuscles settle to the bottom, when the supernatant fluid may 

 be siphoned off; or the blood may be centrifugalized at once and 

 separation of the cellular elements effected in this way. Blood- 

 plasma that has been obtained after the injection of albumoses is 



