300 Organic Substances and Formations. 



a peculiar red colouring matter. All kinds of flesh contain an 

 immense quantity of water, and unless the chief animal tissues 

 and substances are very moist, active life appears impossible, 

 though some creatures may be very nearly dried without being 

 killed. In such a condition they are torpid, from suspended 

 functions. By^drying animal substances their susceptibility to 

 chemical change is destroyed, as is illustrated by the fact that 

 in some parts of the Andes, and in other very dry, cold places, 

 the bodies of the dead shrink into natural mummies, and suffer 

 no decay. 



Ready susceptibility of chemical change is the condition of 

 those substances on which life mainly depends, and the nerve 

 materials exhibit this quality in a high degree. The human 

 brain contains in one hundred parts, about seven of albumen,* 

 five of peculiar fatty acids — one of which, cerebric acid, contains 

 phosphorus — and about eighty of water. Cerebric acid contains 

 no less than five bodies, carbon, hydrogen, nitrogen, phos- 

 phorus, and oxygen, and many other important animal com- 

 pounds are equally complicated. As might be expected from 

 the complex character of the substances we have mentioned, 

 blood, from which they all spring, is remarkable for its 

 numerous and complicated components. Chemists recognize 

 in it four kinds of fatty matter, fibrin, albumen, common salt, 

 and other soluble salts, together with other materials, amongst 

 which iron is conspicuous. We have seen that the chemical 

 composition of animals and vegetables is substantially the 

 same, but the proportion of the various compounds entering 

 into both, vary very much, the animal series being remarkable 

 for the quantity of their highly complex nitrogenous elements, 

 while the hydro-carbons with oxygen prevail in plants. A 

 comparison of fibrin with wood may be interesting and in- 

 structive. The former contains more than half its weight of 

 carbon, about 6 per cent, of hydrogen, about 15 per cent, of 

 nitrogen, about 23 per cent, of oxygen, and small quantities 

 of sulphur and phosphorus. The latter varies a little according 

 to its kind, but a piece of oak will contain about 49 per cent, 

 of carbon, about 6 per cent, of hydrogen, about 43 or 44 per 

 cent, of oxygen, and, in some cases, a little nitrogen, say 

 2 per cent. 



The essential part of wood is its fibre, called in chemical 

 language cellulose. This contains 36 definite portions of 

 carbon, united to 30 definite portions of oxygen, and as many 

 of hydrogen. In a very delicate form, cellulose is digestible 

 and nutritious, but. as soon as it concreted into firm fibres like 

 hemp, cotton, etc., it is no longer fit for the food of human 

 beings. 



* See Miller. 



