188 MR. TOYNBEE ON THE ORGANIZATION AND NUTRITION 



The chorion subjacent to the hoofs of animals presents two different characters, the 

 one being that of numerous fine villosities, the other of compressed lamellae ; these 

 are revived into depressions on the surface of the hoof, and are composed of vessels 

 which terminate in loops, possessing frequently considerable dilatations. 



Hair and bristles, of various kinds, in the neighbourhood of the vascular chorion, ace 

 composed of roundish corpuscles loosely connected ; more remote from the chorion, 

 their substance is harder ; the corpuscles are flattened, and they appear to possess 

 the characters of horn. The chorion, with which the hair is connected, consists of a 

 papilla, which is inserted into the interior of the base of the hair, and of a sheath or 

 capsule which surrounds it ; both the papilla and capsule are supplied with large and 

 numerous blood-vessels, which form loops and dilatations. 



Feathers. — In his elaborate article "Aves," in the Cyclopaedia of Anatomy and 

 Physiology, Professor Owen, after quoting the interesting observations of himself. Sir 

 W. Jardine, Mr. Blyth and Mr. Yarrell, on the changes that take place in the 

 colour of the plumage of birds subsequent to their complete development, says, "Not- 

 withstanding the extra-vascuJar nature of feathers, they are subject to influences ap 

 parently of a vital nature, which occasion a change of colour in them after they are 

 completely formed." 



Feathers near to the vascular chorion consist of corpuscles more or less compressed; 

 further removed from the chorion they are highly compressed, and present a simi- 

 larity to the hair. The chorion to which the feathers are attached presents a pulp and 

 capsule, which have a disposition of vessels analogous to those of the hair. 



The Teeth are now considered to be permeated by an infinity of fine tubes, which 

 are supposed to have the function of conducting from the surface of the vascular 

 pulp, a nutrient fluid, which is distributed over the substance of the tooth. In this 

 way may be explained the manner in which the teeth change their colour during dis- 

 eases, being impregnated by the various fluids circulating in the system*. 



From the preceding observations by myself, and from those made by the physiolo- 

 gists whose writings I have quoted, I think it is established, as a general law in 

 Animal Physiology, that certain tissues are capable of being nourished without the 

 presence of blood-vessels within them : it has been shown that all these tissues are 

 surrounded by large blood-vessels, which appear to have no other function than of 

 supplying to them a nutrient fluid ; and the way in which this nutrient fluid is con- 

 veyed into the substance of these tissues has been also pointed out. 



* Recent investigators have thrown so much light upon the structure and the mode of growth of the Epi- 

 dermoid Class of non-vascular tissues, that (as is apparent) I have added but few new facts in this department 

 of my researches. 



