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PHYSIOLOGY: LOEB AND NORTHROP 
those other natural products which will either supply abundantly the 
deficiencies or act as an ^antidote' to any inherent toxicity. 
1 Hart, E. B., McCollum, E. V., Steenbock, H., and Humphrey, G. C, Wisconsin Exp. 
Sta. Research Bull. No. 17, 1911. 
2 Stepp,W., Zs. Biol., Miinchen, 57, 1912, (135) 62,1913, (405); Hopkins, E.G., /. Phys- 
iol. 44, 425, 1912; Eunk, C, Zs. Physiol. Chem., 88, 1913; (352), 92, 1914, (13); McCollum, 
E. v., and Davis, M., /. Biol. Chem., 15, 1913; (167), 23, 1915, (231); Osborne, T. B. and 
Mendel, L. B. Ihid., 15, 1913, (311). 
3 McCollum, E. v., and Kennedy, C, /. Biol. Chem., 24, 1916, (491). 
4 Hart, E. B., and McCoUum, E. V., Ihid., 19, 1914, (373); McCollum, E. V., and 
Simmonds, N., and Pitz, W., Ihid., 25, 1916, (105); Hart, E. B., Miller, W. C, and 
McCoUum, E. V., Ihid., 25, 1916, (239). 
6 Hart, E. B., Miller, W. C, and McCollum, E. V., Ihid., 25, 1916, (239); McCollum 
E. v., Simmonds, N., and Pitz, W., Ihid., 25, 1916, (105). 
WHAT DETERMINES THE DURATION OF LIFE IN METAZOA? 
By Jacques Loeb and J. H. Northrop 
LABORATORIES OF THE ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH. NEW YORK 
Read before the Academy, April 16, 1917 
1. It can be stated as a fact that most if not all organisms have a 
characteristic duration of life. To give extreme examples, many insects 
have a duration of life measured in weeks only, while the Californian 
sequoia has a duration of life of thousands of years, and in the human 
being the duration of life is proverbially three score and ten. The 
question arises: What determines this characteristic duration of life? 
Biitschli was the first to point out that unicellular organisms have 
an unlimited duration of life and this idea has become very popular 
through Weismann. All recent researches support the correctness of 
this idea. As a consequence we are forced to the conclusion that nat- 
ural death is a phenomenon found almost exclusively in organisms 
which are composed of different organs. The idea that natural death 
is connected with the compound character of organisms is supported by 
two facts; namely, first, the observation that a cutting will survive the 
whole plant, while the cutting if not separated would have died with 
the whole plant. By the method of cuttings the life of the individual 
plant can be prolonged apparently indefinitely. 
The second fact is that if we take pains to transplant certain cells 
from an old organism successively to young organisms, these cells will 
outlive the original individual indefinitely — they are, in other words, 
immortal. The proof can only be furnished with the aid of marked 
cells and Leo Loeb selected for this purpose the cancer cell which is 
easily distinguishable from other cells by its rapid growth. He thus 
