332 THE SOLIDS. 



blood in its vessels. In the contracted state of this mem- 

 brane the slender fibres of the elastic tissue as well as their 

 nuclei are frequently curled up in a spiral manner, an ar- 

 rangement by which any amount of shortening may be secured. 



The contraction of the tissue of the dartos, and indeed of 

 all elastic tissue, is evidently not a physical, but a vital act : 

 this is shown by the relaxation and contraction which it ex- 

 periences in sympathy with the condition of the vital powers, 

 as well as with any causes, as heat and cold, which affect 

 these powers. 



The corpora cavernosa penis and corpus spongiosum urethras 

 are almost entirely composed of blood-vessels, and the 

 peculiarity of these parts consists in the large size of the 

 vessels and in their repeated inosculation. (Plate XLIII. 



fig- 4-) 



In the lungs, the blood-vessels are so numerous, that they, 

 in this case, also constitute the principal portion of the fabric of 

 these organs : this may be beautifully seen in the lungs of 

 the lower reptiles, as the triton and frog. 



Henle has described a peculiar arrangement of the 

 fibres of elastic tissue. " I have already said," he remarks, 

 " that the fibres of the cellular tissue are for the most part 

 united into a number more or less considerable, and thus 

 form flattened bands of different thickness. These bands 

 unite in their turn to produce others larger, or even mem- 

 branes, and thus sometimes they apply themselves paral- 

 lelly to each other ; at others, they cross each other in the 

 most varied directions. When the cellular tissue fills the 

 interstices of organs under the form of a soft mass, easy to 

 displace, and extensible, the bundles may be perceived with- 

 out the least preparation, seeing that they cross and inter- 

 lace in all directions, and that even to the naked eye they 

 represent a network of delicate fibres. The size of the 

 bundles, which I call primitive bundles, or after their 

 origin, the fibres of the cells of cellular tissue vary from 

 the 0-003 to the 0-006 of a line. The majority of the 

 primitive bundles are deprived of special envelope : the fibres 

 may easily be detached, the one from the other, and separate, 



