ANIMAL GRAFTS AND REGENERATIONS. 245 
mark, indeed, that in this case a grafting is made of a whole 
complete organ, with a structure and vascular arrangements 
which may make its development certain, while the trans- 
plantation of a fragment of periosteum or of marrow has 
the effect of isolating and encysting it. 
The most exact and curious experiments that have been 
made in animal graftmg, of late years, are due to Paul 
Bert. ‘This learned physiologist has shown that, if the tail 
of a young rat be cut off and inserted, after flaying it, under 
the animal’s skin, in any part of the body, it adheres to the 
place and continues to develop there. The organ gains 
in size almost as rapidly as in its normal conditions. Bert 
has also practised animal layering. He flays the point of 
a rat’s tail, inserts the end in a hole made beneath the ani- 
mal’s skin, near the head, for instance, and joins the edges 
of the two wounds by stitches at points. The parts placed 
in contact quickly unite, and the tail, thus endowed with 
the shape of a handle, keeps its vitality. If it is then cut 
at any point, it is found that the fragment grafted in at the 
head preserves its physiological properties. The vessels 
are formed again in it, the nerves renew their life, and sen- 
sibility returns by degrees. The rat is thus furnished with 
a sort of trunk as much alive as its other organs. The re- 
turn of sensibility in this trunk proves not only the con- 
nection of the nerve-threads of such an appendix with 
those of the back, but also the possibility of the propaga- 
tion of sensor nerve-action in an opposite direction to that 
it previously followed, that is to say, the power of the 
nerves to carry impressions in a centripetal course as well 
as in a centrifugal one. 
Siamese grafting has been effected by Bert under ex- 
ceedingly interesting conditions. Strips of skin are sepa- 
rated by cutting along the opposite sides of two animals, 
and by means of these ribbons pressed face to face, and 
stitched together, the two subjects are sewed into union. 
