A MANUAL OF PHYSIOLOGY 



CHAPTER I 

 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 com- 

 position: 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 com- 

 pounds 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 ) n may be taken as a type, appear to be always 

 present. Fats, which consist of carbon, hydrogen, and oxygen, and 

 of which tristeaiin, a compound of stearic acid with glycerin, of 

 the formula C 3 H 5 ,3(C 18 H 35 O 2 ), may be given as an example, are 

 often, and certain lipoids, e.g., lecithin (p. 4), are always, found. 

 Finally, water and certain inorganic salts, such as the chlorides and 

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



The Proteins. The constitution of the protein molecule is still un- 

 known ; 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. 354). It has there- 

 fore been suggested that proteins are built up by the linking together of 

 amino-acids, the different proteins differing quantitatively or quali- 

 tatively as regards the amino-acids present (E. Fischer). Thus serum- 

 albumin and egg-albumin yield no glycin or glycocoll (amino-acetic 

 acid, CH 2 .NH 2 .COOH), while glycin is constantly found among the 

 cleavage products of serum-globulin. And while leucin (a-amino* 



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