88

ANIMAL SUBSTANCES.

It is likewise very frequently found in considerablequantity in plants, combined with organic acids ; hencethe ashes of plants commonly contain a portion ofcarbonate of lime, which is formed in a similar mannerto the carbonate of potash already described (261).

265. Magnesia is very often found associated withlime, more especially in the state of phosphate of mag-nesia (179).

266. The ashes of many plants contain a trace ofoxide of iron, and occasionally also of the oxide of man-ganese.

267. The bodies of all living animals contain a consi-derable quantity of water ; when this is evaporated byheat, there remain certain substances, which may bereadily separated from each other in consequence of thedifferent properties which they possess, just in the sameway that we can separate the various substances whichcompose plants (223).

268. The constituents of the bodies of animals maybe naturally divided into the earthy or inorganic mat-ters, such as the bones, and the organic substances, ofwhich the softer parts of animals are composed.

269. Animal substances, for the most part, are rathermore complicated in their nature than vegetable sub-stances ; they almost all consist of oxygen, hydrogen,carbon, and nitrogen ; in consequence of the presence ofthis latter element, they are more liable to decay (245)than most vegetable substances are.

270. The principal substances which compose the