Apeil 19, 1907] 



SCIENCE 



627 



coTirses. The polishing was accomplished by 

 movement in the water-courses, aided by the 

 carbonic acid and the calcium carbonate car- 

 ried in solution. (The polishing work of such 

 waters may be seen in certain caves in the 

 Copper Queen mine at Bisbee, Ariz.) 



The topography of the region, the character 

 of the pebbles, their depth below the surface, 

 their relation to the water-courses, the small- 

 ness of the joint openings at the surface and 

 the absence of similar pebbles on the surface 

 all make it improbable that the pebbles came 

 from the surface. 



E. T>. George 



SPECIAL ARTICLES 



UPON THE TEACHING OF THE SUBJECT OF 



RESPIEATION ' 



At least three totally distinct definitions of 

 the term respiration are expressed or implied 

 in current literature. These and varying 

 shades of meaning are often confused even 

 in the same discussion, and the result is very 

 unsatisfactory. 



The first definition occurs in works upon 

 the physiology of the higher animals. Among 

 the different senses in which respiration is 

 there used, one refers to the functions of lungs 

 and giUs, processes essentially secondary and 

 which take place far away from the cell. 



A second definition is found in general 

 works and especially in botanical ones, namely, 

 that respiration is an exchange of gases, a 

 sort of commerce between the cell and its 

 environment. A majority of our botanical 

 text-books give a categorical definition some- 

 thing as follows. " Respiration is the taking 

 in of oxygen and the giving out of carbon 

 dioxid and water." To this is often joined 

 the idea that the amount of carbon dioxid 

 given oS is equal to that of oxygen absorbed, 

 that in fact the oxygen which enters is the 

 same as that which reappears immediately as 

 carbon dioxid, and not seldom, some emphatic 

 and sweeping statement that the living sub- 

 stance must obtain oxygen somehow all the 

 time. 



A third and entirely distinct meaning is 



"Read before the Botanical Society of America 

 at the New York meeting, December, 1906. 



given to the word in more scientific works 

 such as Pfeffer and in at least two American 

 text-books, namely, that respiration is a vital 

 operation taking place within the cell, a meta- 

 bolic process in which energy is released and 

 which is ordinarily indicated by the gaseous 

 exchange mentioned in the last definition. 

 The steps of this process are not well known, 

 but any discussion of them seems to include 

 also anaerobic or intramolecular respiration 

 and certain kinds of fermentation. 



The confusion in words is inconvenient 

 enough, but there is back of it a confusion of 

 ideas which is more serious, and by which the 

 teaching of the subject is more or less im- 

 paired. From the standpoint of the teacher it 

 is imperative that the subject be cleared up 

 somewhat. However, before dealing with the 

 appropriateness of definitions, let us briefly 

 look over the phenomena which we have to 

 deal with. The most common forms of ap- 

 paratus used by teachers in this country in 

 the study of respiration are U tubes or thistle 

 tubes in which flowers or germinating seeds 

 are placed. The end holding the seeds is 

 sealed and the other end placed in some 

 reagent which will absorb carbon dioxid or 

 oxygen, or both, or in mercury which will 

 absorb none of the atmospheric gases and 

 serve as a control. With such arrangements 

 it is easy to obtain satisfactory and instruct- 

 ive proof that oxygen is absorbed and carbon 

 dioxid given off. If the idea were carried no 

 further all would be well, but there is a 

 temptation to bring in also quantitative re- 

 sults, and, pointing out the fact that caustic 

 potash rises about one fifth of the volume of 

 the tube, to imply that the oxygen contained 

 has been combined in the activity of the plant 

 into an equal amount of carbon dioxid. Re- 

 markable quantitative result is it not, that if 

 in an enclosed space there is a plant absorb- 

 ing oxygen and a reagent absorbing carbon 

 dioxid, the result should be a reduction of 

 volume to that of the nitrogen present? 



Ordinary experiments and bright pupils are 

 a combination which is likely to cause a dis- 

 turbance in formal ideas of respiration. Sup- 

 pose, for instance, that three U tubes with 

 germinating peas in the sealed end are set up. 



