THE STORY OF THE BODY'S CONSTITUTION 9 



manufacture or secrete the gastric juice of the 

 stomach, those which manufacture the sweetbread 

 juice, or those which secrete the saliva of the 

 mouth (Fig. 4) or the tears supplied by the tear 

 glands of the eyes. More important still, in respect 

 of the duties they perform, are nerve cells, those 

 which constitute the units of the nervous system 

 (Fig. 5) or governing system of the body, amongst 

 which fall naturally to be included the brain cells. 



Fig. 4. SECTION OF SALIVARY GLAND 



Showing cells lining the duct (b), and others 

 situated in the gland substance. 



We may regard the living matter of which nerve cells 

 are composed as representing the highest form of 

 protoplasm which is known. If we are to judge the 

 character of living matter by the duties it performs, 

 it is obvious that the living matter of a brain cell, 

 engaged in the work of bodily government, must 

 be of a vastly superior character to that which 

 devotes its energies to the manufacture of bile or 



