io§2.] Experimentation in Biology . 539 
reindeer having eaten lemmings (Brehm), horses and oxen 
entered water to catch fish (Burdach), parrots taken to 
blood-sucking, and so on. Again, not only do morpholo- 
gical changes occur ; thus the gastric juice of herbivorous 
animals is normally less aCtive than that of carnivorous 
species, but by causing an herbivore to absorb peptogens 
the stomach may be rendered functionally carnivorous, ex- 
periment showing that peptones prepared by them, and 
injected into the stomach or blood of a carnivore, are assi- 
milated, and not passed into the urine (see Letourneau ; 
Biology, “ Library of Contemporary Science ”). The expe- 
riments of Reaumur, who introduced pieces of meat en- 
closed in perforated metal tubes into the gizzards of birds, 
and found they were dissolved, — and of Spallanzani, who 
performed artificial digestion by employing gastric juice 
from the living body, — upset the trituration theory of 
Borelli, Boerhaave, and Pitcrairn, which had itself displaced 
the fermentation theory of Hilmon. By experiment we 
know that limitation of diet to one vegetable may kill a 
rabbit in about a fortnight ; but as such condition of poverty 
has perhaps never occurred in Nature, the experiment loses 
its value for our purpose : this remark largely applies to the 
starvation experiments on the higher animals by Chossat, 
but those on Amphibia and snails are not without interest ; 
thus a snail loses only one-eleventh part of its weight after 
a six weeks’ fast, according to Burdach. 
Prof. Semper devotes a chapter to “ Other Conditions.” 
The chief of these are pressure and electricity, but observa- 
tions from Nature are alone recorded. Nevertheless the 
study of the effects of pressure is valuable in connection 
with the environment of fish; for instance, M. Cailletet 
ereCted apparatus in which fish were placed under a pressure 
of 400 atmospheres. The effeCfs of eleCtric shocks upon 
animals have been made known to us by Dr. Richardson’s 
researches: ecchymosis, loss of hair, &c., may result, 
though it is doubtful, as Prof. Semper remarks, whether any 
other effeCt is produced in Nature by electricity save death, 
while here individuals, not species, are exterminated. Ex- 
periments have been made with regard to other influences, 
especially the aCtion of poisoned atmospheres : the scientific 
value of these must be sought in the success attending any 
attempt to accustom an animal permanently to reside in a 
similar medium. Experiments on the effects of ozone have 
been chiefly interesting as showing the peculiar relative 
powers of endurance in various animals : thus mice live 
longer than rats, rabbits than guinea-pigs ; but enough has 
2, N 2 
