154 PHYSIOLOGY OF NUTRITION 



lose their power with temperatures about ioo°C. Trommsdorffi called the 

 former "abgetotet" and the latter "abgestorben."'' If plants are killed in the 

 proper way, the enzymes of their tissues still exhibit their characteristic proper- 

 ties, in the presence of air, water, and substances that are poisonous to bacteria 

 but not injurious to the enzymes. It may seem, at first thought, that such 

 plants should continue to carry out their general life-processes in the same man- 

 ner as do living ones, so that the latter might be hard to distinguish from the 

 former. Deeper study, however, reveals important diSerences. When plants 

 are killed without the destruction of their enzymes the physiological system of 

 the cells appears to become completely disarranged, with the destruction of the 

 interrelations that obtain between the different constituents of the living cell. 

 In the living organism the different cells and cell components appear to be bound 

 together and interrelated so as to form a harmonious whole —somewhat as our 

 solar system is unified — but the component units of a dead cell, even though its 

 enzymes still retain their proper powers, appears to be a mass of unrelated compo- 

 nents enclosed within a common membrane; a tissue composed of such cells is 

 without the interrelations that make it a living tissue. Just as an atom of 

 radium breaks down into its component particles, so does the living cell break 

 down at death, it being the largest physiological unit of the organism. The 

 following important differences may be noted between the enzymatic processes 

 of dead cells and those of living ones.^ 



1. There is no correlation in activity between the different enzymes in dead 

 cells. In living cells an enzyme remains active only so long as the products of its 

 activity are used. In dead cells the activity of an enzyme is not regulated by 

 that of the other enzymes. Enzyme activity is apt to be prolonged even after 

 its products have ceased to be removed. 



2. In dead cells enzymes are decomposed by other enzymes. This was 

 clearly demonstrated by the experiments of Petrushevskaia.' As is well known, 

 the respiratory activity of living yeast is increased by a rise in temperature. On 

 the other hand, the enzymatic activity of zymin (yeast killed with acetone) is 

 retarded by increased temperature. So, for example, lo g. of zymin produced 

 706.5 mg. of CO2 at from 22 to 23°C., while only 285.3 nig. were formed at from 

 33 to 34°C. This difference, amounting to 59.7 per cent., may be explained by 

 supposing that the velocity of protein decomposition in the acetone preparation 

 increases with higher temperature. According to Petrushevskaia only 35.9 per 

 cent, of the protein nitrogen of the zymin was decomposed in three days at 

 from 15 to i6°C., while 81.5 per cent, was broken do^vnin the same time at 

 32°. The proteolytic enzyme appears to decompose the zymase, which is of 

 protein nature. 



' Trommsdortf, Richard, Ueber die Bezieliungen dor Gram'sohen Pirbung zu chemisoheu Vorgangen in 

 der abgetateten Hefezelle. Centralbl. Bakt. //, 8: 82-87. 1902. 



2 Palladin, W., Die Eigentiimlichkeiten der Fermentarbeit in lebenden und abgetateten Pflanzen. 

 Fortschr. naturw. Porsch. i : 253-268. 1910. 



' Petruschewsky, Anna, Einfluss der Temperatur auf die Arbeit des proteolytischen Ferments und der 

 Zymase in abgetateten Hefezellen. Zeitsch. physiol. Chem. so: 251-262. 1906-1907. 



' While there is some usage of killed and dead, as corresponding to these German words, 

 such a usage seems undesirable and is here avoided. — Ed. 



