.YET? i -o us TISS UE. 



69 



into syntonin or acid-albumen, and by the action of dilute alkalies into alkali- 

 albumen. Muscle, which is neutral or slightly alkaline in reaction when at rest. 



FIG. 43. Non-striated elementary fibres 

 from the human colon, a. Treated with 

 acetic acid, showing the corpuscles. 6. 

 Fragment of a detached fibre, not touched 

 with acid. 



FIG. 44. Muscular fibre-cells from human 

 arteries. 1. From the popliteal artery. A. 

 without ; B. with acetic acid. 2. From a 

 branch of the anterior tibial. a. Nuclei of 

 the fibres. Magnified 350 times. 



is rendered acid by contraction, from the development probably of sarcolactic 

 acid. After death muscle also exhibits an acid reaction, but this appears to be 

 due to post-mortem change. 



NERVOUS TISSUE. 



The nervous tissues of the body are comprised in two great systems the 

 cerebro-.ipinala.ndi the sympathetic; and each of these systems consist of a central 

 organ, or series of central organs, and of nerves. 



The cerebro-spinal system comprises the brain (including the medulla oblongata), 

 the spinal cord, the cranial nerves, the spinal nerves, and the ganglia connected 

 with both these classes of nerves. The sympathetic system consists of a double 

 chain of ganglia, with the nerves which go to and come from them. It is not 

 directly connected with the brain or spinal cord, though it is so indirectly by 

 means of its numerous communications with the cranial and spinal nerves. 



Both these nervous systems are composed of an aggregation of tissue-elements 

 termed neuron*, each of which consists of a nucleated cell whose protoplasm is 

 prolonged into a varying number of processes, one of which is usually of consid- 

 erable length and forms the essential part of a nerve-fibre. The cell-bodies have 

 a tendency to be associated together in more or less definite masses, such as the 

 spinal and sympathetic ganglia, the central portion of the spinal cord, the floor 

 of the medulla oblongata. the cortex of the cerebellum and of the cerebral hemi- 

 spheres, and the various ganglia distributed through the different parts of the 

 brain. These masses present macroscopically a grayish appearance, which con- 

 trasts strongly with the pure Avhite color usually shown by the nerve-fibres, so 

 that it is customary to speak of the nervous system as composed of two substances, 

 the gray matter and the u'hite or fibrous matter. The nerve-fibres of the sympa- 

 thetic system, however, usually lack the constituent which gives the ordinary 

 fibres their white appearance, and they consequently have a grayish color. 



The gray substance is distinguished by its dark reddish-gray color and soft 

 consistence. It is found in the brain, spinal cord, and various ganglia, inter- 

 mingled with the fibrous nervous substance, and also in some of the nerves of 

 special sense, and in gangliform enlargements which are found here and there in 

 the course of certain cerebro-spinal nerves. It is composed, as its name implies, 



