960 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



during hunger shown in the ratio above, has been ascribed to the decomposi- 

 tion of the bones. 1 Thus Munk found on Cetti, who lived many days without 

 food, a ratio as low as 4.5:1. In starvation the brain and nerves do not 

 decrease in weight, so the protagon can hardly yield any great amount of phos- 

 phoric acid (Voit). Casein and other nucleo-albumins, when fed, are oxidized 

 and furnish phosphoric acid for the urine. 



CARBON, C = 12. 



This element is found combined in every organism, and in many decom- 

 position-products of organized matter. Elementary carbon occurs as lamp- 

 black, diamond, and graphite, the two latter having their origin from the action 

 of high heat on coal. Carbon occurs combined in coal, petroleum, and natural 

 gas, which are all products of the decomposition of wood out of contact with the 

 air. Further it is found in vast masses, principally consisting of calcium car- 

 bonate, having their origin from sea-shells. The maintenance of life depends, as 

 will be shown, on the small percentage of carbon dioxide which is contained in the 

 atmosphere. Lavoisier believed that compounds of carbon were all products 

 of life, formed under the influence of a " vital force," which was a property 

 of the cell. It is now known that almost every constituent of the cell may be 

 prepared from its elements in the laboratory without the aid of any " vital 

 force " whatever. Notwithstanding its loss of strict scientific significance, the 

 old term " organic " for a carbon compound is still in vogue, and conveniently 

 describes a large number of bodies which are treated under the head of " or- 

 ganic chemistry," while the term " inorganic " is applied to the rest of the 

 chemical world. 



Elementary Carbon. This bums only at a high heat. It is unaffected 

 by the intestinal tract. This is shown by the fact that diamonds have been 

 stolen by swallowing them, and that finely divided particles of lampblack pass 

 unchanged and unabsorbed to the feces, coloring them black (proof that the 

 intestinal canal does not absorb solid particles). If lampblack be eaten with a 

 meal its appearance in the feces may be used as a demarcation line between the 

 feces belonging to the period before the meal, and the period subsequent to it. 

 Carbon unites directly with hydrogen, oxygen, and sulphur only. 



Carbon Monoxide, CO. This gas is a product of the incomplete combus- 

 tion of carbon, is present in illuminating gas, and burns on ignition to carbon 

 dioxide. It is usually prepared by heating oxalic acid with sulphuric acid, 



COOH 



the carbon dioxide being removed by passing through calcium hydroxide. 



Properties. A. colorless, odorless gas. Inspired, it unites with the blood 

 to form a carbon-monoxide haemoglobin (Hb-CO). This is a very stable 

 bright-red compound which may even be boiled without decomposing. Ani- 

 1 See Voit : Hermann's Handbuch, 1881, vi. 1, p. 79. 



