236 PHYSIOLOGY AT THE FARM. 



spinal centre, and, like the parts on which they are distributed, 

 present a remarkable symmetry on the two sides of the body. 

 The ganglionic nerves, called also sympathetic, are distributed 

 chiefly on the viscera and blood-vessels, in which the natural 

 sensibility is obscure and the movements involuntary. They 

 are distinguished also from the cerebro-spinal nerves by their 

 colour, which is greyish or reddish, by a much less degree of 

 symmetry in their arrangement, and in particular by their con- 

 nection with very numerous ganglia. Branches of communica- 

 tion pass from the spinal nerves of the cerebro-spinal, and from 

 several of the cerebro-spinal nerves originating within the skull 

 at a short distance from their roots to join the ganglionic sys- 

 tem of nerves, so that the two systems mutually give and 

 receive nervous filaments. 



In the nervous system there are contained, besides its pro- 

 per substance, enclosing membranes, areolar tissue, and blood- 

 vessels. The nervous substance is distinguished into a white 

 substance and a grey substance, called also cineritious sub- 

 stance. 



The chemical constitution of the cerebral substance is still 

 far from being perfectly known. The brain plainly contains a 

 large proportion of albumen in the uncoagulated form ; its 

 peculiar composition, however, appears to be due to the pre- 

 sence of a solid fatty acid named cerebric acid, in which phos- 

 phorus exists, and to a liquid oily acid called oleo-phosphoric 

 acid, in which also phosphorus is detected. Besides these two 

 acids and albumen, there are found cholesterine, and the ordin- 

 ary fats named stearine and oleine. 



In 100 parts of human brain there are about 7 parts of 

 albumen, 5 parts of the several kinds of fatty substances, 

 and 80 of water. 



Under the microscope the nervous substance is found to con- 

 sist of two distinct structural elements namely, fibres and 





