286 E. ROBERTS AND D. G. SIMONSEN 
the rat) that steady-state concentrations of small molecules reflect the enzymatic 
differentiation of normal tissues and the similarities found in tumors agree with 
GREENSTEIN’s generalization’? based on enzyme assays: “No matter how or from 
which tissues tumors arise, they more nearly resemble each other chemically than 
they do normal tissues or than normal tissues resemble each other”. Typical results 
in Figs. 1-4 show comparisons of chromatograms of extracts of epidermis and normal 
mouse liver with those obtained from equal fresh weights of a transplanted squamous- 
cell carcinoma and hepatoma, respectively. 
Results obtained in a study of extracts of tissues from human, monkey, dog, cat, 
guinea-pig, rabbit, rat, mouse, opossum, chicken, alligator, snake, turtle, frog, 
salamander, and a wide variety of marine organisms in our laboratory by this tech- 
nique! have shown that in a given species at a particular stage of development each 


Figs. 5-12. Chromatograms showing constancy of patterns of free amino acids in extracts of 
brains (37.5 mg) of eight Swiss mice. y-Aminobutyric acid, 22. 
References p. 348/349 
