HELIOTROPISM OF ANIMALS 67 
Decaying meat has the same attractive effect on the larva of 
flies. If such animals are in a test-tube containing decaying 
meat, and the tightly fitting cork is loosened a little, the 
animals which were crawling between the meat and the open 
end of the tube turn and go back toward the meat. I mois- 
tened a small area on a plate by rubbing it with decaying meat. 
I placed some half-grown larvee which I had taken from the 
meat in the middle of this moist surface. They at first crept 
toward the room side of the plate, but turned when they 
came to the boundary of the surface smeared with the putrid 
meat, and remained within it. Not until half an hour later, 
when the spot had dried completely, did they leave it. 
When I merely moistened a spot on the plate with pure 
water, the larve did not remain on it. 
When I removed the animals from a cadaver and placed 
them on a glass plate, and brought a piece of decaying meat 
into their neighborhood, the animals crept toward it, even if 
in so doing they were obliged to move toward the window; 
this occurred, however, only when the animals were in the 
immediate neighborhood of the meat. When they were 
more than a centimeter and a half away from the meat, they 
were no longer attracted by it; they then followed the direc- 
tion of the rays of light and starved in the neighborhood of 
food. Animals which had not yet tasted food were also 
attracted by the decaying meat. Fat, even when foul, 
attracted the animals only slightly or not at all; this is very 
remarkable, as the female flies are also more readily attracted 
by meat than by fat. I often placed a piece of horse flesh 
and a piece of horse fat side by side in the sun. Ata time 
when the flesh was covered with eggs, the fat was almost free 
from them. It seems, therefore, as though the same chemical 
stimulus which attracts the larve causes the flies to deposit 
their eggs. Decaying cheese also attracted the larve, but 
ammonia and assafcetida were without effect. Some volatile 
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