13 



oxvgen. 



may 



metres 



bable tbat tlie direct metabolism of tbe protoplasm plays a 

 considerable part in tliem. 



A calculation has been made in order to give an idea of the 

 volume of carbonic acid given off in these experiments. The 

 amount produced per hour by 100 grammes of ripe grapes at 

 30^ C. was 5-2 mg. This would measure about 2-9 cubic centi- 



and the grapes at this rate would give off a volume of 

 carbonic acid equal to their own bulk in about 32-6 hours, while 

 the cherries in the first experiment would produce a corre- 

 sponding amount in 11-8 hours. 



Other experiments were made on the keeping quality of fruits 

 in air and in other gases. In one case apples of one variety 

 were placed in jars of air, nitrogen and hydrogen, and left for 

 13 days. In each jar som-e apples were fairly ripe, and others 

 somewhat green. At the end of the experiment the apples in 

 air were in very good condition^ t while those in nitrogen and 

 hydrogen had lost their red colour, and had turned brown, both 

 their appearance and flavour being much as in half-baked apples. 

 This effect in nitrogen and hydrogen was shown not to be due to 

 micro-organisms, but to the anaerobic respiration of the fruit. 

 This shows the necessity of aeration when apples are kept for a 

 considerable time at the temperature of the experiment, which 

 was 21^ to 230 C. 



Another experiment was made with peaches, and it was found 

 that they became brownish and acquired a bad flavour in the 



mens was greatly 



p 



ompare 



In two experiments referred to above it was found that ripe 

 cherries respired much more rapidly than ripe grapes in the 

 ratio of 14-2 to 5-2:;:. In view of the better keeping properties 

 of grapes as compared with cherries, it is suggested that the rate 

 of evolution of carbonic acid may be more or less proportional 

 to the rate of spoiling of ripe frnit, and this may also be pro- 

 portional to the enzyme content of the frnit, since the processes 

 concerned are probably chiefly due to the action of enzymes.'' 

 Hence, if the factors controlling the production of enzymes were 

 sufficiently understood, additional means might perhaps be found 

 for improving the keeping quality of fruit. 



It is desirable that further experiments should be made, m 



manner 



of carbonic acid by various kinds of fruit at different tempera- 

 tures much lower than 30° C. Definite and comprehensive 

 information on respiration at rather low temperatures would no 

 doubt be very useful in relation to cold storage. 



Feeble respiration takes place at 0° C, and even at — 2° to 

 -4° C. and it continually increases as the temperature rises, until 



* These figures are obtained by reckoninfr the fruit as having a specific 

 sravity of 1"097, this being tbe value obtained with a sample of grapes, 

 t 'Except two out of seven, which appeared to have developed brown rot. 

 + This was in both cases in a continuous current of air at 30 C. 

 I As suggested by the fact that they are largely independent of oxygen. 



