LYMPH AXD CHYLE. 37 



Gases of the Blood. When blood is exposed to the vacuum of an air-pump, 

 about half its volume is given off in the form of gases. These are carbon dioxide, 

 oxygen, and nitrogen. The relative quantities in 100 volumes of arterial and 

 venous blood, at C. and 1 in. pressure of mercury are shown in the accom- 

 panying table : 



Oxygen. Carbon dioxide. Nitrogen. 



Arterial blood, 16 vols. 30 vols. 1 to 2 vols. 



Venous blood, 6 to 10 vols. 35 vols. 1 to 2 vols. 



Roughly stated, they are as follows : Carbon dioxide about two-thirds of the 

 whole quantity of gas, oxygen rather less than one-third, nitrogen below one- 

 tenth (Huxley). The greater quantity of the oxygen is in loose chemical com- 

 bination with the haemoglobin of the blood-corpuscles, but some part is simply 

 absorbed, just as it would be by water. The carbon dioxide is in a state of chem- 

 ical combination with the salts of the serum, especially the sodium, with which it is 

 combined partly as a carbonate and partly as a bicarbonate. The nitrogen is 

 unimportant. It (or at least the greater part of it) is merely absorbed from the 

 atmosphere under the pressure to which the blood is exposed, and can therefore be 

 mechanically removed. 



Blood-crystals. Haemoglobin, as stated above, when separated from the blood- 

 corpuscles, readily undergoes crystallization. These crystals, named hcemoglobin 

 crystals, all belong. Avith the exception of those obtained from the squirrel, to the 

 rhombic system. In human blood they are elongated prisms (Fig. 4, A). In the 



FIG. 4. Blood-crystals. A. Hsemoglobin crystals from human blood. B. Hsemin crystals from blood treated 

 with acetic acid. c.'Hamatoidin crystals from an old apoplectic clot. 



squirrel they are hexagonal plates. Other crystals may be obtained by mixing 

 dried blood with an equal quantity of common salt, and boiling it with a few drops 

 of glacial acetic acid. A drop of the mixture placed on the slide will show the 

 crystals on cooling. These are named hcemin crystals, and consist of small acic- 

 ular prisms (Fig. 4. B). Occasionally in old blood-clots a third form of crystal is 

 found, the ha?niatoidin crystal (Fig. 4, c). 



LYMPH AND CHYLE. 



Lymph is a transparent, colorless, or slightly yellow fluid, which is conveyed 

 by a system of vessels, named lymphatics, into the blood. These vessels take 

 their rise in nearly all parts of the body from the interstices of the connective 

 tissue, and take up the fluid contained in these spaces and return it into the 

 veins close to the heart, there to be mixed with the mass of the blood. The 

 greater number of these lymphatics empty themselves into one main duct, the 

 thoracic duct, which passes along the front of the spine and opens into one of the 

 large veins at the root of the neck. The remainder empty themselves into a 

 smaller duct, which terminates in the corresponding vein on the opposite side of 

 the neck. 



Chyle is an opaque, milky-white fluid, absorbed by the villi of the small 

 intestines from the food, and carried by a set of vessels similar to the lymphatics, 

 named lacteah, to the commencement of the thoracic duct, where it is intermingled 



