SECTION III. 



Cellular Chemistry. 



I. CHEMICAL CONSTITUENTS OF CELLS. 



In the consideration of the structure of organized bodies we found 

 that, no matter how complicated their form, all organized matter was 

 capable of being resolved into a unit of organization, which we termed, 

 with Briicke, an elementary organism or cell. 



Cells, therefore, are the simplest schematic form to which all the 

 various forms of organized bodies are capable of being reduced. Chemi- 

 cal investigation of organized bodies further shows that they are equally 

 simple as regards their elementary composition. Of the sixtj'-five chemi- 

 cal elements only seven enter with any degree of constancy into the forma- 

 tion of organic compounds ; these are oxygen, nitrogen, hydrogen, carbon, 

 sulphur, phosphorus, and iron. By far the greatest number of all organic 

 compounds are composed only of the three elements, carbon, hydrogen, 

 and oxygen, varying in the different relative proportions of each. In 

 one group, represented by the organic acids (succinic acid, C 4 H 6 4 ), even 

 if we assume that all the hydrogen present is associated with oxygen in 

 the proportion to form water, there always remains a considerable excess 

 of oxygen unaccounted for. In the second group, represented by the 

 carbo-hydrates (glycogen, C 6 H 10 O 5 ), we have twice as much hydrogen as 

 oxygen, or, in other words, the oxygen and hydrogen exist only in the 

 proportion to form water. In the third group, composed of these ele- 

 ments, carbon, hydrogen, and oxygen, and represented by the fatty acids 

 (oleic acid, CigH^O.,), if we suppose that all the oxygen is united with 

 the hydrogen in the proportion to form water, we have still a consider- 

 able excess of hydrogen unaccounted for. Such bodies are, therefore, 

 termed hydro-carbons. 



In another group of organic compounds, and one of the most im- 

 portant of the constituents of cells, we find nitrogen associated with 

 carbon, hydrogen, and oxygen. Such a group we would therefore term 

 the nitrogenous, in contradistinction to the non-nitrogenous. 



To this group belong the highly complex organic products (complex 

 as regards their molecular arrangement), which contain sulphur and occa- 

 sionally phosphorus, and still more rarely iron, and which are represented 

 by the albuminous bodies ; the nitrogenous organic acids and bases, the 



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