Chap. 7 TISSUES 123 



Nervous tissue is mentioned here because it is one of the four main types 

 of tissues. Since nerve cells are peculiarly related and interdependent as a 

 whole system, the general discussion of them is given with The Nervous Sys- 

 tem, Chapter 16. 



Fig. 7.16. Nerve cell from the cerebral cortex or gray 

 matter of a rabbit. The axon gives off numerous branches 

 and then enters the white substance, within which it 

 extends a long distance. Only a small part of the axon is 

 shown in the drawing, a, axon; b, white substance; c, 

 collateral branches of axon; d, descending or apical 

 dendrite; p, its terminal branches at the outer surface 

 of the brain (After Ramon y Cajal. Courtesy, Maximow 

 and Bloom: Textbook of Histology, ed. 6. Philadelphia, 

 W. B. Saunders Co., 1952.) 



Important Reactions in Tissues 



Inflammation. The defense reaction of living tissues to an unfavorable 

 condition such as an infection is evidenced by inflammation. Its general results 

 are redness, swelling, heat, and pain at or near the site of the injury. The 

 region becomes congested and swollen by an accumulation of body fluids 

 and their associated cells. There is increased activity of these cells; this and 

 the greater supply of blood produce a local heat rise. The congestion with 

 pressure on the nerve endings results in soreness and pain. 



There is an efficient cellular defense against inflammation. Cells which 

 produce antibodies or antitoxins and may be phagocytic are scattered every- 

 where in loose connective tissue and in the blood and lymph. In the loose 

 connective tissue there are many capillaries from which increased numbers 

 of leucocytes migrate to the inflamed areas (Fig. 7.18). The neutrophils 

 move in first and act quickly; monocytes enlarge and, along with the now 



