DISTRIBUTION OF HEMOGLOBIN AND ALLIED SUBSTANCES 



mass actions, does not involve intrinsic changes, and is in effect a passive 

 phvsico-mechanical function or a means of transport and storage. 



The first type must be considered as representing a property that is 

 possessed in common by all parts of the protoplasmic mass, at least until 

 our knowledge is different from that of the present. As to the second type, 

 the photosynthetic exchange is almost wholly confined to chlorophyllous 

 substances, while the chemosynthetic exchange occurs chiefly in the entire 

 absence of chlorophyl. The view held by many that chlorophyl is per se 

 a primary respiratory photosynthetic substance was long ago shown to be 

 untenable. Isolated chlorophyl has been proved to be absolutely inert in 

 the exchange of C0 2 and O, and the cytoplasm of the chloroplastid has been 

 found to be functionless in photosynthesis in the absence of chlorophyl, as 

 in etiolated plants, in which what feeble photosynthesis may be present is 

 attributed to the etiolin. In fact, the chloroplastid is a vital mechanism 

 which consists, broadly speaking, of cytoplasm in some form of union with 

 chlorophyl and etiolin, which is capable of exercising its normal photosyn- 

 thetic functions only when all of the essential structural and physiological 

 units are intact, and whose peculiar photosynthetic properties, therefore, 

 are dependent upon some cooperative and inseparable relationship between 

 the cytoplasm and the pigments. The exact structural relations of the 

 cytoplasm and chlorophyl are unknown, but the chlorophyl appears to be 

 held in a cytoplasmic stroma in vacuolar form. Moreover, normal functional 

 activity can be maintained only so long as normal relations exist between 

 the chloroplastid and its habitat. The isolated chloroplastid soon becomes 

 functionless; and notwithstanding the very close resemblance of the 

 chloroplastids of the higher forms of plant life, it is questionable if, like the 

 erythrocyte, these structures of one genus could continue to exist as living 

 units in an individual of another genus. 



Whether or not chlorophyl is to be looked upon as being in the nature 

 of an energizer or sensitizing agent in relation to the cytoplasm is yet a 

 matter of speculation among physiological botanists. It is of particular 

 interest in this connection to note that chlorophyl itself may be energized, 

 for it has been shown in Florida that phycoerythrin, which is not assimi- 

 lative and which apparently does not enter into either physical or chemical 

 union with chlorophyl, markedly modifies the assimilatory curve of chloro- 

 phyl in relation to the spectral colors, and so greatly increases the energy 

 of chlorophyl that a very small quantity of chlorophyl will give rise to 

 energetic photosynthesis. While iron seems to be essential in the forma- 

 tion of chlorophyl, the latter is nevertheless iron-free, and the suggestion 

 that the reducing action of the chloroplastid may be due to iron is regarded 

 by the botanist as being absolutely untenable. In fact, apart from the 

 necessity of iron in the formation of chlorophyl, this metal does not seem 

 to be of more importance as a constituent of the chloroplastid in photo- 

 synthesis, or in respiration, than potassium, or magnesium, or certain other 

 inorganic constituents. 



The foregoing facts are, as a whole, strikingly paralleled in hemoglobin 

 and the erythrocyte, the chief difference being found in the ways in which 



