Polarity in Organic Elements. 363 



enough to Dermit a halting walk. But the most remarkable modifica- 

 tion of this order occurs in un-united fractures. False joints are often 

 formed joints which rudely simulate the hinge structure, or the ball- 

 and-socket structure, according as the muscles tend to produce a mo- 

 tion of flexion and extension, or a motion of rotation. In one case, ac- 

 cording to Rokitansky, the two ends of the broken bone become smooth 

 and covered with periosteum and fibrous tissue, and are attached by lig- 

 aments that allow a certain backward and forward motion ; and in the 

 other case, the ends similarly clothed with the appropriate membranes, 

 become the one convex and the other concave, are enclosed in a cap- 

 sule, and are even in some cases supplied with synovial fluid. " ( Biol- 

 ogy, 1-187.) 



Animal Grafting. A graft on a tree is a parasite living on the vital 

 fluid of its host, yet transforming it to a homogeneity with its own tissues. 

 The same in animal grafting, a particular tissue transferred to another 

 person or to another place in the same person, retains its own nature and 

 may continue to nourish itself and add to its size at the expense of its 

 host, yet preserving its individuality. " The cells of the choroid of the 

 eye placed beneath the skin of an animal preserve their vitality in that 

 new region, and there they even become the starting point for a more or 

 less extensive formation of similar cells." Transfusion of blood is the 

 transfer of red blood cells from the arteries of one animal to those of 

 another. The blood of a mammal may be transferred to a frog and con- 

 tinue to live there and remain distinguishable from the others. It is 

 easy to graft upon the comb of a cock either spurs taken from the same 

 bird or teeth from a mammal. A periosteal membrane, separated from 

 the bone and grafted under the skin, will produce a new bone on its 

 under side even a few cells of the rudimentary layer adhering to that 

 membrane ({. e. the cartilaginous layer) will grow into bone when 

 grafted. ' ' Goujon has brought about the production of bone by graft- 

 ing marrow. " The growth of a small bone was produced in a few months 

 by inserting a few medullary cells ( marrow cells ) under the skin of a 

 dog. These bony parasites will, after a time, become re-absorbed be- 

 cause they have no regular nerve and vascular supplies to keep them 

 growing and renovated otherwise a new nose might be made of bone. 

 The growth of teeth is from a little sac or follicle. There are two prin- 

 ciples involved in the growth, the enamel and the dentine, each of which 

 consists of cells of its own kind, and neither will produce the other. If 

 a follicle be removed from a very young puppy, it may be grafted and 

 grow on the back of an old dog, to a perfect tooth. If the germ of the 

 dentine or ivory alone be grafted, that will grow and produce ivory, 

 but the enamel germ alone will not grow. Paul Bert cut off a rat's 

 tail and grafted it into another part of the body, where it grew success- 



