268 PHYSIOLOGY OF NUTRITION. 



plant material in tlie apparatus, we shall still find that the titre 

 of the baryta water has changed. This change, for 1 hour and 

 75 c.c. of baryta water, corresponds with 0'5 to I'O mgr. of 

 Carbon dioxide. The experimental error, whose magnitude is 

 frequently to be determined in the manner indicated, may in 

 many cases be entirely neglected, since, as a matter of fact, the 

 differences in Carbon dioxide evolution arising from individual 

 peculiarities in the plants under observation are very often greater 

 still. 



If it is required to determine the quantity of Carbon dioxide 

 produced, not in intramolecular but in normal respiration, we 

 work with the same apparatus, merely taking away the Kipp's 

 apparatus, the wash bottle containing Potassium permanganate, and 

 the U-tube with Silver nitrate solution. If we are experimenting' 

 with structures which soon wither (e.g., corolla leaves or delicate 

 flowers), it is well to let the air traverse a vessel containing moist- 

 glass wool before it reaches the worm. To make the researches, 

 we first draw air through the apparatus for one and a half to two 

 hours by means of the aspirator (3 1. per hour). By this time the 

 air in the respiratory chamber will be sure to have come to a 

 stationary condition as regards the quantity of Carbon dioxide 

 which it contains. We now put in the first baryta tube, after an 

 hour the second, and so forth. To make sure that during the in- 

 troduction of the baryta tubes no Carbon dioxide escapes from the 

 respiratory space, it is well to have a stop-cock (or clip) at the 

 top of the spiral tube, and to close -this and also the stop-cock H" 

 before putting in a fresh tube. (The stop-valve Sch is unneces- 

 sary.) As to the precautions to be observed in investigations 

 proceeding uninterruptedly for days, see the cited treatise of 

 Sachsse (1872) and my own (1875). 



With reference to researches intended to determine the ratio 

 between the amount of Carbon dioxide produced by any given 

 plant material during internal respiration and that produced 



during normal respiration ' the conditions being otherwise 



similar, the following particulars are to be noted : We put- 

 together the whole apparatus, leaving out only the Hydrogen 

 generator. Having drawn air through for one and a half hours by 

 means of the aspirator, the determination of the amount of Carbon 

 dioxide produced in normal respiration begins. After one to two 

 hours, we connect up the Kipp's apparatus, pass a rapid current 



