6 VETERINARY PHYSIOLOGY 



of the tissue constitute the processes of Neerobiosis, and their 

 study is of importance in pathology. 



III. Chemistry. It is impossible to analyse such an ever- 

 changing substance as protoplasm, and although what is left 

 when these chemical changes are stopped can be examined, 

 such analyses give little insight into the essential nature of 

 the living matter. 



That substances of great complexity take part in the con- 

 stant whirl is shown by the analyses of what is left after 

 death. Five or six elements carbon, hydrogen, oxygen, 

 nitrogen, sulphur, and phosphorus are present, and these 

 are linked together to form molecules of enormous size. 



Water is the most abundant constituent of protoplasm, 

 amounting, as it does, to about 75 per cent. 



The Solids, constituting the remaining 25 per cent., con- 

 sist chiefly of a series of bodies closely allied to one another 

 and called " chief substances " or Proteins. In addition to 

 these, certain inorganic salts are found in the ash when 

 protoplasm is burned, indicating the presence of POTASSIUM 

 and CALCIUM along with PHOSPHORUS and SULPHUR. The 

 inorganic salts, and especially their kations, appear to be of 

 considerable importance in maintaining the activity of proto- 

 plasm, and their possible mode of action will be considered 

 later. Small and varying quantities of FATS, and of CARBO- 

 HYDRATES, with traces of a number of other organic sub- 

 stances which need not here be enumerated, are also usually 

 present. 



Of these substances the Proteins alone have to be con- 

 sidered here, since they constitute the really important part 

 of the material. 



PROTEINS 



White of egg or the juice of meat may be taken as examples 

 of such proteins dissolved in water with some salts. If the 

 salts be separated, and the water carefully driven off at a low 

 temperature, a pure protein is left. 



(A) Physical Char-aeters. The proteins from the residue of 

 living matter the Native Proteins, as they may be called 

 have a white, yellow, or brownish colour. In structure they 



