A MANUAL OF PHYSIOLOGY 



INTRODUCTION 



LIVING matter, whether it is studied in plants or in animals, 

 has certain peculiarities of chemical composition'and structure, 

 but especially certain peculiarities of action or function, which 

 mark it off from the unorganized material of the dead world 

 around it. 



Chemical Composition of Living Matter. Although we 

 cannot analyze the living substance as such, we can to a certain, 

 but limited, extent reconstruct it, so to speak, from its ruins. 

 When subjected to analytical processes, which necessarily kill it, 

 living matter invariably yields bodies of the class of proteins, 

 exceedingly complex substances, which have approximately the 

 following composition : Carbon, 51*5 to 54*5 per cent. ; oxygen, 

 20-9 to 23-5 per cent. ; nitrogen, 15-2 to 17 per cent. ; hydrogen, 

 6-9 to 7-3 per cent., with small quantities of sulphur. Nucleo- 

 proteins, which are compounds of ordinary proteins with nucleic 

 acids, a series of sulphur-free organic acids rich in phosphorus, 

 are constantly met with. Certain carbo-hydrates, composed of 

 carbon, hydrogen, and oxygen (the last two in the proportions 

 necessary to form water), of which glycogen (C 6 H 10 O 5 ) rt may be 

 taken as a type, appear to be always present. Fats, which con- 

 sist of carbon, hydrogen, and oxygen, and of which tristearin, a 

 compound of stearic acid with glycerin, of the formula 

 CgH^fC^H^Cy, may be given as an example, are often, and 

 certain liquids, e.g., lecithin (p. 4), are always, found. Finally, 

 water and certain inorganic salts, such as the chlorides and phos- 

 phates of sodium, potassium, and calcium, are constantly present. 



The Proteins. The constitution of the protein molecule is still 

 unknown ; but when proteins are broken down by the action of 

 ferments, such as exist in gastric and in pancreatic juice, or by 

 chemical methods for example, by boiling with dilute acids the 

 most important of the cleavage products are various amino-acids 

 (P- 33 2 )- I* has therefore been suggested that proteins are built up 

 by the linking together of amino-acids, the different proteins 

 differing quantitatively or qualitatively as regards the amino-acids 

 present (E. Fischer). Thus serum-albumin and egg-albumin yield 



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