BLOOD TISSUE 



87 



a^^^c^jrtbri 



clenolrite^ 



-aacon 



shecxth. 



the dendrites, nerve cells connect with each other. The axon 

 is the process which connects the nerve cell with a structure 

 remote from the cell body. 



If one hears a sound and walks toward 

 it, an axon has carried the sound from 

 the ear to a nerve cell in the brain. By 

 means of dendrites, a connection w^as set 

 up with another nerve cell which in turn 

 carried the message to muscle cells. The 

 muscle cells contracted so as to make 

 walking possible. Axons vary in length : 

 some are microscopic while others may be 

 as long as two or three feet. The cell 

 body is always of microscopic dimensions. 

 Nerve cells attain the highest development 

 of irritability. They are the highly sensi- 

 tive cells of the body. They receive mes- 

 sages, transmit them, and regulate the 

 responses to these messages. Nerve tissue ^. , ^, 



^ ^ sometimes very long, the axon. 



will be studied in greater detail in a later Although the ceii body, cyton. 



° is microscopic, the axon, also 



microscopic in diameter, may 

 be two or three feet long. 



- terminal brandies. 



The unit of nerve structure 

 is called a neuron. This cell 

 has several processes, one 



chapter. 



Blood tissue. Blood is so highly fluid 

 that it is not usually considered a tissue. A tissue has been 

 defined as a group of similar cells, and blood, consequently, may 

 be considered a tissue since it consists of groups of similar cells. 



Problem. Study of blood tissue. 



Press the finger near the tip until blood congests. Prick the end of the finger 

 with a needle that has been passed through a flame to sterilize it. Touch a 

 cover glass to the drop of blood on the finger ; invert the cover slip on a glass 

 slide. Mount under the low, then under the high power of the microscope. 



I. Describe the shape, size, and color of the more numerous cells seen. 

 These are the red corpuscles. 



II. Examine all the substance under the microscope carefully and find 

 an occasional irregularly shaped cell. This is a white or amoeboid corpuscle. 



