8 BRAIN AND SPINAL CORD. PART m. 



the muscular energy, led M. Matteucci to suspect that 

 a chemical action must take place in the interior of a 

 muscle during its contraction ; and he found by experi- 

 ment that there actually is what he calls a muscular 

 respiration, namely, that the muscles themselves absorb 

 oxygen, and give out carbonic acid gas and nitrogen 

 when contracted. This kind of respiration is more or 

 less common to all animals ; if impeded, the blood is 

 imperfectly oxygenized, and loss of animal heat is the 

 consequence. The heat that is perpetually escaping 

 from animals is replaced, by the combustion of the 

 carbon of the tissues or of the food with the oxygen 

 inhaled by the lungs and the skin. 



In the highest class of animal life the brain is at once 

 the seat of intelligence and sensibility, and the origin 

 of the nervous system. In the lower animals intelli- 

 gence and sensibility decrease exactly in proportion 

 to the deviation of their nervous system from this high 

 standard. The forms of the nervous system are more 

 and more degraded as the animals sink in the scale of 

 being, till at last creatures are found in which nerves 

 have only been discovered with the microscope ; others 

 apparently have none, consequently they have little or 

 no sensibility. 



The brain and the spinal cord enclosed in the ver- 

 tebree of the backbone form a nervous system, which in 

 the vertebrated creation is equal to all the contingencies 

 and powers of these animated beings, but is beyond 

 all comparison most perfect in the human race. The 

 brain alone is the seat of consciousness, for the spinal 

 cord, though intimately connected with it, and of a 

 similar 6 mysterious albuminous electric pulp,' appears 

 to have no relation to the faculties of perception and 

 thought, yet it is essential to the continuance of 

 life. It is a distinct nervous centre which generates 

 muscular energy in man and animals corresponding to 



