August- 22, 1919] 



WlEIfCE 



191 



cliroinidlal apparatus, Or the so-called INissl 

 substance. It is a true metabolic pigment. 



The genesis of the melanin in depression 

 explains satisfactorily its occurrence in con- 

 ditions of frank disease as well as in abnormal 

 physiological conditions. It happens in dis- 

 ease because the majority of abnormal stimuli 

 are essentially depressant. Melanin is also an 

 almost invariable concomitant of old age. 

 Eecognizing the dual forms of senility, senility 

 of depression and senility of excitation, the 

 melanin is introduced by depression, which is 

 an almost inevitable factor in the production 

 of the combined state as it occurs in an organ- 

 ism under ordinary conditions. In the sep- 

 arate experimental production, pigment is the 

 most concrete point of difference between the 

 two forms of senility. 



Of particular interest to anatomists is the 

 exploding of the tradition that melanin pig- 

 ment is a natural structural constituent of 

 certain nerve cells. Such old terms as sub- 

 stantia nigra and locus cseruleus apparently 

 have given tliis idea its greatest plausibility. 

 Also the bulk of human anatomical material 

 is from old or diseased individuals. Still no 

 two investigators have ever agreed, either on 

 its time of development, or on the places of 

 its consistent location. As a matter of fact, 

 the melanin may be entirely absent from an 

 adult nervous system, and even if present in 

 some cells of a part, it may be absent in 

 others. Such pigment-free animals are how- 

 ever scarce, for few have escaped depression. 

 Extending this negative deduction to man, 

 the cells supposed to be pigmented are the 

 most obviously homologous with those of 

 lower animals naturally pigment free, and it 

 would be a most unique anomaly if man's 

 differentiation alone should endow him with 

 the useless. 



The lipochrome, or as it has been more com- 

 monly designated in doubt of its origin, the 

 fat-holding or fat-combined pigment, has been 

 the object of more active investigation and 

 discussion in recent years. Its characteristic 

 is' its reaction to the fat stains, Sudan III. 

 and scarlet red. The prevailing opinions have 

 been either that it is some sort of a by-product 



of cell metabolism, an " Abnutzung " or 

 '■ wear-and-tear " pigment, as designated by 

 Lubarsch, or that it is a more specific product 

 of fat or fatty acid metabolism, the lipofuscin 

 of Borst and Hueck. 



The lipochrome turns out to be an ex- 

 ogenous pigment derived from the carotinoid 

 pigments, namely, the carotin and xanthophyll 

 of plants, which are ingested with the food. 



It might seem surprising that so direct a 

 connection has escaped identification. It has 

 not escaped a surmise, as the original trans- 

 ferrence of the word lipochrome from botany 

 testifies, but the difficulty was that certain of 

 the earlier microchemical tests for lipochrome 

 in plants failed in their application to animal 

 tissues. The development of the chemistry 

 of the pigments is bringing a progressive 

 identification between plants and animals. 

 The identification started with the isolation in 

 crystalline form of xanthophyll from the yolk 

 of the hen's egg and of carotin from the 

 corpus luteum by Willstatter and Escher. 



The knowledge of the relation of these pig- 

 ments to animal metabolism has been ex- 

 tended chiefly by Palmer and Eckles and later 

 by Palmer alone. They have shown that the 

 natural yellow pigment of the milk fat, body 

 fat, corpus luteum and blood serum of the cow 

 is identical with carotin, while xanthophyll 

 predominantly, with some carotin, colors the 

 egg yolk, body fat and blood serum of the 

 hen. Further Palmer has demonstrated a re- 

 markable species difference. Species with 

 colored fat, such as the cow, horse and hen, 

 carry the pigments in the blood serum; spe- 

 cies with colorless fat, such as sheep, swine 

 and goats, do not carry the pigments in the 

 blood serum under the most favorable con- 

 ditions. 



Palmer is also carrying on some conclusive 

 feeding experiments on chickens. Chickens 

 deprived from birth of carotinoid pigments 

 show absence of the yellow pigment in their 

 skin, fat, egg yolk and blood serum. Given the 

 pigments in their food, the color is restored. 

 If any fowl, yellow from its natural food, be 

 deprived of pigment, the color fades, though 

 the process takes some months. 



