470 OF NUTRITION. 



tional of this, with 5 Oxygen and 1 water. The following table represents the composi- 

 tiun of the fatty acids, and of the compounds just mentioned. 



Stearic Acid 68 Carbon, 66 Hydrogen, 5 Oxygen. 



viargaric Acid .... 34 Carbon, 33 Hydrogen, 3 Oxygen. 

 Oleic Acid 44 Carbon, 39 Hydrogen, 4 Oxygen. 



Stearin e. Margarine. Oleine. 



1 atom of Glycerine 6 c, 7 H, 5 o c, 7 H, 5 o 6 c, 7 H, 5 o 



2 atoms of Acid 136 c, 132 H, 10 o 68 r, 66 H, 6 o 88 c. 78 H, 80 



Water (1 or 2 atoms) .... 2 H, 2 o 1 H, 1 o 2 u, 2 o 



Total 142 c 141 H, 17 o 74 c, 74 H, 12 o 94 c, 87 H, 15 o 



619. Besides the support, combined with facility of movement, which Fat 

 affords to the moving parts of the body, it answers the important purpose of as- 

 sisting; in the retention of the animal temperature by its non-conducting power; 

 and the still more important object of serving as a kind of reservoir of com- 

 bustible matter against the time of need ( 730). Herbivorous animals, whose 

 food is scanty during the winter, usually exhibit a strong tendency to such an 

 accumulation during the latter part of the summer, when their food is most 

 rich and abundant ; and the store thus laid' up is consumed during the winter. 

 Fat appears to be deposited only when there is an excess in the alimentary 

 matter introduced into the body, of non-azotized compounds which may be 

 converted into it ( 433). But the ingestion of a large quantity of these in the 

 food, is by no means sufficient for the production of Fat ; for they may not be 

 absorbed into the vessels ; and, if absorbed, there may be a want of power to 

 generate Adipose tissue, so that they would accumulate injuriously in the 

 blood, if not drawn off by the Liver ( 664). Hence some persons never be- 

 come fat, however large the quantity of oily matter ingested ; and it is in such 

 persons that the tendency to disorder of the Liver from over-work is most 

 readily manifested ; hence they are obliged to abstain from the use of fat- 

 producing articles of food. 



620. We have next to speak of the Epidermic tissues, which were long 

 described as altogether inorganic in their character, but which are now known 

 to have the same origin with all the rest. The Epidermis consists of a series 

 of flattened scale-like cells, which, when first formed, are spheroidal, but which, 

 gradually dry up, their nucleus still remaining visible. These form several 

 layers, of which the deeper can be seen very distinctly to possess the cellular 

 character ; whilst the exterior layers are scaly ; and between these, all stages 

 of transformation can be traced. The outer layers are continually being thrown 

 off by desquamation ; and new ones are as constantly being formed below, 

 from organizable matter exuded by the basement membrane. What has been 

 termed the rete mucosum is simply the last formed portion of the Cuticle : 

 and in this we do not find completely formed cells, but granular nuclei, in 

 progress of development. The Epidermic membrane, which is formed by 

 this aggregation of cells, is pierced by the excretory ducts of the sebaceous ancl 

 sweat-glands, and also by the shafts of the hairs. Its layers become more 

 numerous, as the surface is rubbed ; the corium being thus stimulated to an 

 increased exudation. The Chemical constitution of this tissue is of peculiar 

 interest, in relation to that of the Horny appendages which it bears. Recent 

 analysis has shown that the membranous Epidermis of the sole of the foot, and 

 the compact Horny matter of which Nails, Horn, Wool, and Hair are com- 

 posed, have the same constitution ; the formula of all being 48 c, 30 H, 7 N, 

 17 o ; this bears a close relation to Protein, and may be regarded as consisting 

 of one proportional of Protein with 1 atom of Ammonia, and 3 of Oxygen. 

 The Epidermis covers the whole exterior of the body, not excepting the con- 

 junctiva and cornea ; where, however, it undergoes a modification in its cha- 



