246 NATURE AND LIFE. 
After a few days the connection has grown complete, and 
we have such a pair as the Siamese twins. Bert kept two 
white rats thus banded together for more than two months; 
but they lived on such bad terms that at the end of that 
time it was necessary to separate them. By poisoning one 
of two animals of such a brace, the other is poisoned also, 
thus proving that there is complete mutual circulation of 
blood. Bert effected like graftings between the white rat 
and the Norway rat, and between the white rat and the Bar- 
bary rat. He attempted to perform them between animals 
of different species—between a rat and a Guinea-pig, be- 
tween a rat and a cat—but the success was never complete ; 
only the beginning of adherence was obtained. Still this 
failure seems to depend less on the incompatibility of the 
tissues themselves than on the difficulty of keeping animals 
so little disposed to live harmoniously together in the ne- 
cessary state of quiet. Once more, Balbian succeeded in 
uniting two fragments of tails taken from two different 
young bull-heads, so as to obtain a physiological adhesion 
for a certain length of time. 
If the interest attached to such experiments is rather 
philosophic than practical, a point to be considered here- 
after, this is not the case with those which obtain as results 
what are called epidermic grafts. These indeed have had 
the privilege of attracting the highest degree of attention 
from physiologists, and particularly from surgeons. We 
owe to a Swiss surgeon, Reverdin, formerly an interne of 
the Paris hospitals, the discovery and the first application 
of these. Whenever, after a surgical operation, a burn or 
a wound, the skin over a certain extent of surface is de- 
stroyed, the void produced is filled up only very slowly 
by means, of a growth of scar-tissue. In spite of the 
use of the most judicious: methods of dressing, the ex- 
posed surface is never restored but with difficulty. In 
seeking a remedy for this grave inconvenience, Reverdin 

