238 PHYSIOLOGY AT THE FARM. 



The gelatinous fibres are also termed organic or grey nerve- 

 fibres ; they exist in great numbers in the sympathetic nerve 

 and in small proportion in many of the cerebro-spinal nerves. 

 They are found associated with tubular or white fibres, giv- 

 ing a grey colour to the nervous cords in which they predomi- 

 nate. A doubt, however, has arisen if these be true fibres, 

 it being maintained that they belong to the class of envelop- 

 ing structures, and that in reality they are allied to the areolar 

 tissue. 



The following quotation from Professor Bennett's ' Outlines 

 of Physiology ' points to the modern use of several terms liable 

 to be misunderstood : 



" 1. The brain proper is that portion of the encephalon situ- 

 ated above the corpus callosum. 



" 2. The spinal cord is divided into a cranial and a vertebral 

 portion. 



" 3. The grey matter evolves, and the white conducts, ner- 

 vous power. 



" 4. Contractility is the property peculiar to fibrous texture, 

 whereby it is capable of shortening its fibres. Motion is of 

 three kinds contractile, dependent on muscle ; diastatic, de- 

 pendent on muscle and spinal cord ; voluntary, dependent on 

 muscle, spinal cord, and brain. 



" 5. Sensibility is the property peculiar to nervous texture, 

 whereby it is capable of receiving impressions. Sensation is 

 the consciousness of receiving impressions." 



Blood-Vessels. The blood-vessels consist of arteries and 

 veins and capillaries of pulmonary arteries and pulmonary 

 veins and pulmonary capillaries. 



Arteries are endowed with considerable strength and with a 

 very high degree of elasticity, being extensible and retractile 

 both in their length and width. When cut across they ex- 

 hibit, even when empty, an open orifice ; the veins, on the 



