628 



SCIENCE 



[N. S. Vol. XXV. No. 642 



the open ends being in pyrogallol, caustic 

 potash and mercury, respectively. The pryo 

 rises rapidly by absorption of oxygen till it 

 occupies about one fifth of the volume, the 

 potash slowly does the same as the plants 

 absorb the oxygen and give off carbon dioxid 

 till it also reaches the one-fifth mark and the 

 mercury does not rise at all. After some days 

 the experiment looked upon as a perfect suc- 

 cess is ready to be taken down. Theoretically, 

 over the mercury also the oxygen has been ab- 

 sorbed and its place taken by carbon dioxid. 

 Some student, not knowing any better, con- 

 cludes to demonstrate that fact by introducing 

 potash solution through the mercury. At once 

 the mercury begins to rise in the tube, carry- 

 ing the potash before it. The student watches 

 to see it stop at the one-fifth mark and is 

 astonished to see it continue to mount until 

 it has reached two fifths or even more. Then 

 the best the teacher can do is to clumsily ex- 

 plain that here is something he had not 

 meant to demonstrate; that this is intra- 

 molecular respiration, that carbon dioxid has 

 been produced in quantities and that the mix- 

 ture of carbon dioxid and air has bubbled out 

 through the merqury, some of the nitrogen 

 thus escaping. Now it will at once be urged 

 that some other seeds than peas should have 

 been used for the experiment. But one may 

 at least inquire why. Peas are living things 

 and they are convenient. Moreover, if seeds 

 in any considerable bulk are employed over 

 mercury, the teacher must choose the seeds 

 very carefully indeed if the idea of an equal 

 exchange is not to suffer. If a series of ob- 

 jects are used, alterations of volume will 

 occur in nearly all. In chrysanthemum 

 flowers and peas the volume increases. In 

 beet, turnip and timothy seed the volume 

 diminishes. Facts such as these have long 

 been knovm. It is well known, for example, 

 that in oily seeds generally, oxygen absorp- 

 tion at first outruns production of carbon 

 dioxid. Now after such a brief and frag- 

 mentary consideration of the experimental 

 side, let us take up the question of definitions. 

 In regard to the first definition (that respira- 

 tion refers to the functions of lungs and gills) 

 it may be merely noted that it is of applica- 



tion only in the case of differentiated animals 

 and the question of use must therefore be left 

 to students in that field. It may be pointed 

 out in passing, however, that respiration in 

 this sense is so firmly imbedded in literature 

 that it will probably retain the meaning it has, 

 and that this meaning is so distinct that it 

 will be little source of confusion. For the 

 botanist the discussion must be between the 

 following definitions and here confusion of 

 thought arises very easily. 



In regard to the second definition (that 

 respiration is taking in oxygen and giving out 

 carbon dioxid) it may be observed that it is 

 easy of demonstration and is remarkably clear 

 of statement and these features have probably 

 given it its wide currency. But when we press 

 for the conception lying back of the definition, 

 for the idea which the words convey, it seems 

 to be little more than a physical process of 

 diffusion. On this account a telling objection 

 can be raised. Granting that the gaseous ex- 

 change is easy to demonstrate and that the 

 definition is exceedingly clear, which the 

 writer is freely willing to do; granting that 

 only aerobic respiration need be referred to 

 in general teaching, which the writer is unwill- 

 ing to do, it is still open to the fundamental 

 criticism that it turns the student's attention 

 away from the vital and really important 

 process to a superficial and physical one. For 

 far and away the most important idea in the 

 teacher's subject matter is this : The living 

 substance must have energy; it can get it 

 only by working changes in the compounds 

 within reach in such a way as to release 

 energy. If oxygen is at hand these changes 

 are largely those of oxidation. If oxygen is 

 lacking the cell will find another way. To 

 define respiration then as a gaseous exchange 

 is to turn away from the all-important process. 

 In this connection it may also be noted that to 

 imply in addition that the carbon dioxid pro- 

 duced is equal to the oxygen absorbed amounts 

 to positive error as does also the hard and fast 

 statement that all living matter must obtain 

 constant supplies of oxygen. 



In regard to the third definition it may be 

 observed that it referadto processes which are 

 somewhat obscure anaVhich are, after all. 



