COMPARATIVE STUDIES ON RESPIRATION XXII. 
THE EFFECT OF LACTIC ACID ON THE 
RESPIRATION OF WHEAT 
Edith Philip Smith 
(Received for publication November 9, 192 1) 
Respiration in plants and animals involves a continuous series of linked 
reactions, of oxidative character, the end products being carbon dioxide 
and water. The reaction proceeds by stages, and though the actual steps 
may be unknown, many substances have been suggested as intermediate 
products. The hypothesis that the introduction into a respiring system, 
from without, of an excess of any one of the substances which are supposed 
to be intermediate stages in the metabolism, should accelerate the rate of 
production of carbon dioxide, forms a good basis of trial on which to test 
these suggested substances. On account of its frequent occurrence and 
apparent importance in animal metabolism, lactic acid was chosen as the 
sub'ect of these experiments. 
In dealing with animals, the effect of muscular action on the rate of 
production of carbon dioxide has to be taken into account. In plant 
material there are no such complications; it is easy to secure seedlings at a 
stage when the root system is well developed while the shoot has not yet 
begun to show green. With long roots and abundance of root hairs there 
can be no question as to the successful penetration of the reagent, which 
is an important point. Wheat was accordingly chosen as the material for 
these experiments. It was germinated with aseptic precautions, and used 
when the roots were about two inches long and well supplied with root hairs. 
The method used for studying the respiration was that described by 
Osterhout,^ using phenolsulphonphthalein as indicator. The normal rate 
of respiration (in distilled water) was taken as the reciprocal of the time 
required to change the indicator from pH 7.36 to pH 7.09, and was expressed 
as 100 percent. The actual time varied from 30 seconds to i minute, ac- 
cording to the age of the seedlings. 
After taking the normal rate of respiration, the machine was stopped 
and a solution of lactic acid in distilled water was substituted for the dis- 
tilled water in the flask containing the seedlings. The same volume, usu- 
ally 100 cc, was used in each case. The first effect was a depression in the 
rate of respiration, due to the necessity of saturating with carbon dioxide 
the volume of fresh liquid introduced into the closed system. This ''satu- 
^Osterhout, W. J. V. Jour. Gen. Physiol, i : 17-22. 1918. 
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