228 LIFE: ITS NATURE AND ORIGIN 



gentisic acid apparently appears because of the blocking, at this 

 stage, of the normal oxidation of tyrosine and phenylalanine, 

 which are normal constituents of many proteins. Normal persons 

 completely oxidize the acid, and perfusion through normal liver 

 converts it into acetoacetic acid. It was shown by H. D. Dakin 27 

 that alkaptonuria patients can fully catabolize p-methylphenyla- 

 lanine and p-methoxyalanine, which cannot form quinoid deriva- 

 tives; he believes that inability to catabolize homogentisic acid is 

 associated with increased formation of the quinoid intermediate 

 from which it is derived. 



Detoxication, the route whereby organisms rid themselves of 

 certain poisonous substances, also varies with the changing cata- 

 lytic and chemical nature of the animal. Thus fowls eliminate 

 phenylacetic acid and its homolog, benzoic acid, by combining 

 them with ornithine, while all mammals combine benzoic acid 

 with glycine (amino-acetic acid) and eliminate it as hippuric acid. 

 However, Sherwin and Thierfelder, 28 found that though the lower 

 mammals, including monkeys, combine phenylacetic acid with 

 glycine and eliminate it as phenaceturic acid, man couples phenyl- 

 acetic acid with glutamine and eliminates it as phenylacetylgluta- 

 mine. But experiments on the chimpanzee by Prof. Francis W. 

 Power of Fordham University showed that this "man-ape" elimi- 

 nates phenylacetic acid in the same manner as does man. Here 

 too, as in the biochemistry of muscle, there is a definite relation- 

 ship between chemical mechanisms and the position of the animal 

 in the evolutionary or taxonomic scale. 



In some cases disease may follow photosensitization after intro- 

 duction of stranger molecules. As far back as 1897 O. Raab ob- 

 served that small amounts of acridine exerted a lethal action on 

 paramecia in the presence of light, though the same doses had no 

 effect in the dark. Later, similar effects were seen with eosine, 

 chlorophyll, etc., H. F. Blum describes 29 a number of diseases 

 which develop in grazing animals (sheep, horses, cattle) when they 

 eat certain plants. Among these are fagopyrism due to buckwheat 

 (Polygonum fagopyrum); hypericism, due to St. Johnswort (genus 

 Hypericum); and geeldikkop ("yellow thick head") caused by a 

 South African plant Tribulus, popularly called "devil's weed." 

 In geeldikkop the active material seems to cause liver injury and 

 occlusion of bile, accompanied by retention of phylloerythrin, a 

 chlorophyll derivative. This substance, accumulating in the skin, 

 makes the animal light-sensitive and leads to edema of the head 



