124 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC. 



decomposition, we have compounds, of which the former differs from Gelatine only by the 

 presence of two additional atoms of hydrogen and the deficiency of one of oxygen, whilst 

 the only difference in the latter consists in the presence of one additional atom of hydrogen. 

 Thus the ammoniated Erythroprotid, when exposed to oxygcnation in the lungs, may have 

 its one superfluous atom of hydrogen carried off in the form of water, and will then have 

 the composition of Gelatine ; and the same result will be attained from the ammoniated 

 Protid, by the addition of three atoms of oxygen, which will convert it into Gelatine with 

 two atoms of water. According to this formula, the substances produced from the decom- 

 position of the proteine in blood, merely through the action of the alkali in the serum, and 

 the oxydizing influence of the atmosphere, are carbonic acid, water, gelatinous tissue, and 

 leucin. The carbonic acid passes off through the lungs ; and the water, either by the kid- 

 neys, or by exhalation from the lungs or skin. The Gelatine only requires form, to become 

 Fibrous tissue. Leucin, however, has not yet been found in the body ; and until it shall 

 have been discovered, or the products of its decomposition shall have been detected, any 

 such attempt to explain the formation of Gelatine, must be regarded as altogether theoretical.* 

 c. The relation of Gelatine to the Proteine-compounds is further shown by the fact, that 

 Leucin may be produced from the former, as well as from the latter. When Gelatine is 

 boiled, either with alkalies or with dilute sulphuric acid, Leucin is formed; together with 

 extractive matters, and a peculiar sugar termed Glyricoll. This substance crystallizes in large 

 colourless prisms, which have a sweet taste, and feel gritty between the teeth ; it is soluble 

 in 4 2 parts of water, and is taken up in small quantity by Alcohol. This fact is one of much 

 interest in regard to certain Pathological relations of Gelatine. 



142. The Yellow Fibrous tissue, on the contrary, undergoes scarcely any 

 change by long boiling ; a very small quantity of Gelatine being alone yielded 

 by it; and this being probably derived from the Areolar tissue, by which it is 

 penetrated. It is unaffected by the weaker acids, and undergoes no solution 

 in the gastric fluid ; and it preserves its elasticity for an almost unlimited pe- 

 riod. According to Scherer, the yellow fibrous tissue from the middle coat 

 of the Arteries consists of 48 C, 38 H, 6 N, 16 O ; which (taking Liebig's 

 formula for Proteine) may be regarded as 1 Proteine + 2 Water. When 

 burned, it leaves 1*7 per cent, of ash. 



5. Of Simple Cells, floating in the Animal Fluids. 



143. The red colour, which is characteristic of the Blood of Vertebrated 

 animals, is entirely due to the presence, in that fluid, of a very large number of 

 floating cells, which have the power of forming a secretion in their interior, 

 that is distinguished by its peculiar chemical nature, as well as by its hue. 

 The red Blood-corpuscles (commonly, but erroneously termed globules) are 



flattened Discs, which, in Man and most 



Fig. 27. of the Mammalia, have a distinctly cir- 



cular outline. In the discs of Human 

 ^ blood, when examined in its natural con- 



dition, the sides are somewhat concave ; 

 and there is a bright spot in the centre, 



Tr - ^' ^) ^^) which has been regarded by many as in- 



'-^ ''^ dicating the existence of a nucleus; though 



fs> TSSy^ it is really nothing else than an effect of 



refraction, and may be exchanged for a 

 dark one by slightly altering the focus of 

 the Microscope. The form of the disc 



Red Corpuscles of Human Blood represent- . g mu( . h ^^j , ^.^ entg . 



ed at a, ;is they are seen when rather beyond J i i 



the focus of Ihe microscope ; and at ft as they for the membrane which Composes its CX- 



appear when within the focus. Magnified 400 terior or cell-well, is readily permeable by 

 diameters. liquids ; so as to admit a passage of li- 



quid, according to the laws of Endos- 

 mose, either inwards or outwards, as the relative density of the contents of 



* See Mulder's Chemistry, p. 326. 



