IN THE ANIMAL KINGDOM. 21 



capacities varying from 1.2 to 1.49 c.c. per gram, or a mean of 1.31, which 

 practically is identical with that of hemoglobin, 1.34) certainly throws 

 grave doubts upon the universally accepted fundamental importance that 

 is attached to the metal (iron, copper, manganese) of echinochrome, hemo- 

 globin, chlorocruorin, hemocyanin, pinnaglobulin, etc. While the work of 

 Griffiths has not, as far as we have been able to learn, been confirmed or 

 disproved, it certainly has substantial support in a number of facts, espe- 

 cially the existence of absolutely or practically colorless invertebrates and 

 vertebrates, in which we must from analogy admit the existence of special- 

 ized respiratory circulatory fluids, and also in the known differences in the 

 behavior of the stromata, globin, and proteins generally, on the one hand, 

 and of hematin, on the other, towards and C0 2 . 



Since it is admitted that all living protoplasmic structures are respira- 

 tory, it seems but a short step in evolution to the differentiation of special- 

 ized colorless respiratory substances. While it is not improbable that in 

 some of the lowest forms of life simple forms of respiratory substances 

 exist, it seems that (since chloroplastids, histohematins, hemoglobin, hemo- 

 cyanin, or similar compound bodies are found in very low organisms and 

 throughout all gradations of higher animal and plant life, and from their 

 chemistry) we should look upon a typical respiratory substance as being 

 a compound body which consists essentially of a protein base to which is 

 coupled an acid radical or its analogue, the former being the active respi- 

 ratory component and the latter serving as a go-between and probably in the 

 nature of an energizer. 



Three types of O and CO 2 exchange have been observed : 



(1) The analytic exchange that is characterized by the absorption of 

 and its utilization in the living processes in the breaking down of complex 

 substances and the consequent formation and giving off of C0 2 as an effete 

 product, a form of respiration which involves intrinsic changes: This in 

 all likelihood is common to all forms of living matter (for even anaerobes 

 absorb the last traces of oxygen, and even in plants this type of exchange 

 is directly but little influenced by light). 



(2) The synthetic exchange, photosynthetic and chemosynthetic, the 

 first of which is manifested actively solely through the agency of chloro- 

 phyl and light; which is characterized by the absorption of C0 2 and the 

 giving off of 0; which involves intrinsic changes; and whose intensity is 

 in direct relation to the intensity of light up to the optimal light: This 

 exchange of C0 2 and is believed to take place solely in the chloroplastid, 

 or in some primitive non-cellular form of protein-chlorophyl combination, 

 as in certain phanerogams in which the chlorophyl is normally found in 

 diffused form. In the chemosynthetic exchange, light energy is replaced 

 by energy in chemico-potential form, and the process has no necessary 

 association with chlorophyl. 



(3) The physico-mechanical exchange that goes on in the aeriferous 

 system, intercellular air-spaces, etc., of plants, and in the erythrocytes, the 

 blood plasma, and lymph, etc., of animals: This is dependent essentially 

 upon differences in partial pressures and tensions of these gases and upon 



