4 ANATOMY AND PHYSIOLOGY 



(Combinations frequently used are CC>2 for carbon dioxide or 

 "carbonic acid gas," H 2 for water.} 



Food principles are simple or compound substances, composed 

 of one or several elements. They are broadly classed as, i. con- 

 taining nitrogen, nitrogenous, 2. without nitrogen, non-nitrogenous, 

 and 3. containing only mineral substances. 



TISSUES AND MEMBRANES OF THE BODY 



The simplest form of living matter is protoplasm. A living cell 

 may be nothing more than a definite quantity of protoplasm 

 (called cytoplasm or bioplasm] or it may be more complex, having 

 a nucleus, when it is said to be nucleated, and it may have a 

 nudeolus within the nucleus. A nucleated cell is capable of form- 

 ing new cells by the division of its substance, the division always 

 beginning in the nucleus. 



Sometimes the cell is enveloped by a thin membrane called the cell wall. 



Ifi 



FIG. i. CONNECTIVE-TISSUE 

 BUNDLES OF VARIOUS THICK- 

 NESSES OF THE INTERMUSCULAR 

 CONNECTIVE TISSUE OF MAN. 

 X 240. (Lewis and Stohr.} 



la 



super- 

 posed 

 layers 



FIG. 2. ADIPOSE TISSUE. (Lewis 

 and Stohr.) 



Tissue. Any collection of cells held together by intercellular 

 substance is a tissue. The various tissues of the body are com- 

 posed of cells (and intercellular substance) which are developed in 

 special ways; for example: 



Muscle tissue is composed largely of cells which are highly 

 developed in the power to contract. Contractile tissues (list, p. 83). 



