280 PHYSIOLOGY OF NUTRITION. 



the filter, we first use water saturated with Ba C 3 , then pure 

 water. The Barium carbonate, after being dried and gently 

 ignited, is weighed, and we calculate the corresponding volume 

 of Carbon dioxide at C. and 1,000 mm. barometric pressure. 

 The potash solution employed always contains more or less Potas- 

 sium carbonate to begin with, and the Carbon dioxide of this 

 must be determined by special experiments, and taken into 

 account.* 



With the apparatus described we can deal with many physio- 

 logical questions. Above all it is instructive to follow closely the 

 respiration of germinating seeds. To make the experiments we 

 soak, and lay on the moist blotting-paper, say 2 gr. of wheat 

 grains, 4 gr. of peas, or 1 gr. of Raphanus sativus seeds. After 

 every twenty-four hours the apparatus is opened, the potash solution 

 replaced by new, and the observation continued. The temperature 

 must always be kept very constant, e.g. at 15 or 20 C. 



In experiments with wheat we find, e.g., that 2-2'5 gr. of grains 

 with advancing germination also absorb increasing quantities of 

 Oxygen, and produce increasing quantities of Carbon dioxide. 

 From the fifth day onwards, at a temperature of 20 C., about 

 20 c.c. of Carbon dioxide are produced, and 20 c.c. of Oxygen 

 absorbed, every twenty-four hours. The respiratory ratio is here 

 (and generally in starchy plant structures) approximately 1. 

 In the germination of fatty seeds (e.g. of Raphanus) we find the 

 ratio = 0'6-0'8. They take up relatively much Oxygen, because 

 the fat in germination suffers oxidation, and gives rise to carbo- 

 hydrates. 



1 Literature : Detmer, Physiol.-cliem. Untcrs. ilber Keimung, 1875; Godlewsld, 

 Pringsheim's Jahrb., Bd. 13 ; Moeller, Bericlite d.Deutsclien botan. Gesellscli., Bd. 

 2; Stich, Flora, 1891 ; Bonnier and Mangin, Annal d. sc. nat., Ser. 6, T. 17 

 and 18, give a method of gas analysis, employed also for example by Stich, 

 which in many cases is very serviceable. Further see Bonnier and Mangin, in 

 Annal. d. sc. nat., Ser. 6, T. 19 ; Ser. 7, T. 2. 



* It is still better to determine the Carbon dioxide by the method of titration 

 (see 102). The C0 2 must then naturally be precipitated from the potash solu- 

 tion before and after the experiment by means of Ba C1 2 , the fluid remaining 

 behind being subjected to titration. 



