216 PHYSIOLOGY AT THE FARM. 



coloured blood-cells (blood-corpuscles) are round and flat like 

 a piece of money, or they are described technically as bicon- 

 cave circular discs, smallest in the Napu musk-deer, and 

 largest in the elephant. These coloured blood-cells or blood- 

 corpuscles in mammals have no included body or nucleus. 

 They consist of a vesicle containing a coloured fluid. When put 

 into water they swell out and become globular, losing their 

 colour, and sometimes bursting. Acetic acid renders them 

 transparent and almost invisible. They tend to run together, 

 so as to form cylindrical columns, like piles or rouleaus of 

 pieces of money, the nature of the attraction to which this 

 tendency is due being still unknown. Moreover, these cylin- 

 ders are apt to join together in the form of an irregular net- 

 work. 



The colourless blood-cells are globular, or only slightly flat- 

 tened. They have a distinct nucleus, which, on the addition of 

 acetic acid, shows two or three granules. In mammals they 

 are somewhat larger ; in the other vertebrated orders they are 

 smaller than the coloured blood-corpuscles. They are fewer in 

 number than the coloured blood corpuscles. According to 

 some physiologists, the blood-cells nourish the liquor sanguinis 

 in which they ultimately become dissolved.* 



3. Nerve-Cells or Ganglionic Cells. The nerve or gangli- 

 onic cells, called also ganglionic corpuscles, ganglion glo- 

 bules, and nerve vesicles, constitute one of the two structural 

 elements of the nervous system. The fibres are found univer- 

 sally in the nervous cords, and constitute the greater part of 

 the nervous centres ; the cells or vesicles are confined to the 

 grey matter of the cerebro-spinal centre and the ganglia, and 

 do not exist in the nerves properly so called, unless at the 

 peripheral expansions in some of the organs of special sense. 

 They are very various in figure. For the most part each con- 



* Bennett's 'Outlines of Physiology,' p. 20. 



