144 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



nature. The growing interest in ionization, hydrogen-ion concentration, the role 

 of inorganic salts, of calcium, and so on, all point in this direction. Instead of 

 looking upon the more soUd constituents as the most important, we now regard 

 them as the least. Attention is being directed toward the phosphohpins, which 

 occm- in protoplasm as a diffuse invisible deposit as well as in the form of mito- 

 chondria. According to Mathews (1915, p. 88), they are the most important 

 substances in living matter, "for they are found in all cells, and it is undoubtedly 

 their function to produce, with cholesterol, the pecuhar semifluid, semisoUd state 

 of protoplasm. This latter holds much water in it, but does not dissolve. Indeed, 

 it might be said that the phosphatids with cholesterol make the essential physical 

 substratum of living matter." 



That the substratum is more or less fluid is shown by the free movement of 

 granules and other visible constituents. While many vital phenomena depend 

 on enzymes and we know that they diffuse but slowly, so that it is not essential 

 to assume the existence of compartments to localize their action, there must be 

 some organization in protoplasm of an exceedingly labile sort. It is Ukely that 

 this organization depends upon the pattern of colloidal structure, upon phase 

 differences and transitory and permanent membranes, which make possible the 

 combination and separation of chemical reactions, the orderly sequence of which 

 is at the root of all vital phenomena; and it is this plastic framework which enables 

 the cell to perform its proper functions, in the same way as the bones, comiective 

 tissue, membranes, and so on, permit of integration and division of labor in the 

 body itself and control the form and function of a wonderful mechanism handed 

 down from antiquity. 



THE POSSIBILITIES OF FURTHER STUDY. 



Obviously the investigation of mitochondria is rapidly progressmg beyond the 

 purely descriptive stage. The mere discovery of mitochondria in some new^'genus 

 or species excites but Uttle interest, because we have a very shrewd suspicion that 

 they are present there anjnvay. It would be a great mistake, however, to assume 

 that nothing further remains to be done. We know nothing whatever of mito- 

 chondria in any of the peripheral sense-corpuscles (p. 52), and many other prob- 

 lems suggest themselves. In descriptive work we can profitably let nature be the 

 experimenter and select those forms which aid in the solution of definite questions. 

 For instance, we can direct our attention toward the effect of environmental and 

 other conditions on mitochondria. 



Temperature.— It has been found that mitochondria go into solution when the 

 temperature of the tissue containing them is raised for a few minutes to 45° or 50° C, 

 which is most suggestive with regard to their chemical constitution, the effect of 

 burns, the pathology of fever, and other questions. In this connection the study 

 of succulent plants, Uke Sempervivum, whose internal temperature is said to reach 

 about 52° C, in response to changes in the environment (Jost, 1907, p. 44), as com- 

 pared with others growing in cold climates and in the depth of winter, would afford 

 a new avenue of approach. The flora of hot springs should also be studied. 



