1892.] Comparative Physiology of Respiration. 819 
and burned the carbonaceous waste there found and was 
immediately given out in connection with the carbon with 
which it had united; and as the gas given off in a burning 
candle makes clear lime water turbid, so the breath produces 
a like turbidity. 
But here, as in many of the processes of nature, the end 
products or acts were alone apparent, and while the funda- 
mental idea is probably true that respiration is, in its essential 
process, a kind of combustion or oxidation, yet the seat of this 
action is not the lungs or blood. If the myriads of micro- 
scopic forms are considered, these have no lungs, no blood, 
and many of them even no organs; they are, as has been well 
said, organless organisms, and yet every investigation since 
the time of Vinci and von Helmont, Boyle and Mayow, has 
rendered it more and more certain that every living thing 
must in some way be supplied with the vital air or oxygen, 
and that this is in some way deteriorated by use. The 
nearer investigation approaches to the real life stuff or proto- 
plasm, it alone is found to be the true breather, the true 
= respirer. And further, as was shown long ago by Spallan- 
zani (1803-1807), if one of the higher animals, as a frog, is 
decapitated and some of its muscle or other tissue exposed in 
a moist place it will continue to take up oxygen and give out 
carbon dioxide, thus apparently showing that the tissues of 
the highly organized frog may, under favorable conditions, 
absorb oxygen directly from the surrounding medium, and 
return to it directly the waste carbon dioxide. This proves 
conclusively that it is the living substance that breathes, and 
the elaborate machinery of lungs, heart and blood-vessels is 
only to make sure that the living matter, far removed from 
the external air shall not be suffocated. Still more strange, it 
has been found that if some of the living tissue is placed in 
an atmosphere of hydrogen or nitrogen entirely devoid of 
oxygen, it will perform its vital functions for a while, and 
although no oxygen can be obtained it will give off carbon 
dioxide as in the ordinary air. If it is asked how can these 
things be? the answer is apparently plain and direct. Not as 
the oxygen unites directly with the carbon in the burning 
