PHYSIOLOGICAL 



377 



into daughter-cells. And along with these may be set the power to 

 generate electric currents, a feature of the life of the cell whose 

 significance is not yet fully appreciated. These properties can only 



lmm 



Fig. 50 



Diagram of Various Types of Animal Cells, i. Columnar epithelium: n, nucleus 

 throughout; 2, ciliated epithelium; 3, glandular epithelium, with goblet 

 cells (GC) making mucus (M); 4, a compound branched gland, A a 

 cluster of gland-cells (alveolus), D the efferent duct; 5. smooth muscle- 

 cell; 6, an ectoderm cell of Hydra, with contractile roots (CR); 7, surface 

 view of squamous epithelium; 8, diagrammatic section through a nerve; 

 C, a bundle of nerve-fibres; AR, an artery; V, a vein; L, a lymph vessel; 

 a, external sheath or epineurium; b, supporting matrix of the nerve; 

 c, perineurium around a bundle of nerve-fibres {d) ; 9 and 10, networks 

 of connective-tissue cells, without and with a matrix; 11, a striped 

 muscle-fibre (MF) with alternate dark (D) and light (L) bands; x, a 

 median line across a dark stripe; y, the same across a light stripe; 12, a 

 motor nerve-cell or neuron (NC), giving off short dendrites and a long 

 axon (AF) which gives off a ramifying branch (NBR) and another (NE) 

 nerve-ending on a muscle-fibre. 



be maintained if there is within the cell a constant supply of energy 

 derived from chemical reactions. This supply of energy normally 

 implies nutrition, the supply of food materials; respiration, the supply 



