December 29, 1911] 



SCIENCE 



927 



superior to that of normal pressure. The 

 somewhat increased cost necessitated by a 

 tight receiver is more than offset by the re- 

 duced time involved, by the certainty of the 

 results and by the immediate availability. A 

 suitable receiver of heavy galvanized iron sim- 

 ilar to a kind already on the market, can be 

 manufactured at a reasonable cost. 



But the practical value of this result is no 

 greater than its theoretical bearing. It ap- 

 pears, in the first place, that the role of car- 

 bon dioxid is not associated with its inertness, 

 but is, on the contrary, positive, a conclusion 

 demanded, I believe, by the time relations. 

 How this view may be harmonized by the re- 

 maining heterogeneous mass of facts, at pres- 

 ent available through the efforts of the above- 

 mentioned workers, it is too early to say, but 

 it will prove, I believe, a fruitful suggestion 

 that the explanations demanded are to be 

 found in the relation of the heterogeneous 

 reagents to the colloids, and therefore in the 

 colloidal-chemical reactions, rather than in 

 the better understood chemical relations. One 

 may not overlook the capital fact that other 

 of the ripening processes are hastened by car- 

 bon dioxid, but in different degrees, suggest- 

 ing the effect of a general catalytic agent. 

 An exception, however, is to be noted in the 

 cessation of color changes. A fruit, which is 

 yellow when subjected to carbon dioxid, does 

 not subsequently change to the usual deep 

 orange of the normally ripened. 



From my study of the tannin cells them- 

 selves it emerges that the increase in rigidity 

 of the tannin-masses, a slow process under 

 ordinary conditions, is hastened under normal, 

 and still more under supranormal pressures of 

 carbon dioxid, but is preceded, by a relatively 

 brief period, hy the completion of non-as- 

 tringency. From this it may, for the present, 

 be inferred that the disappearance of soluble 

 tannin is connected with the coagulation of 

 the associated colloid, and that the role of 

 the acid, carbon dioxid, is, directly or indi- 

 rectly, the cause of this coagulation which 

 proceeds up to some, at present, unknown 

 limit at a rate related to the amount of acid 

 available. That, by coagulation, the physico- 



chemical condition of the colloid, and its con- 

 sequent behavior toward tannin, may be 

 changed finds an analogy, perhaps not too 

 loose for my purpose, in the behavior of the 

 micropylar colloid stopping the micropyle in 

 the egg of Fundulus. According to the view 

 of Jacques Loeb (1911) this colloid becomes 

 " tanned " in the course of one or two days if 

 in the surrounding water certain salts are 

 present, thereby rendering the micropylar 

 plug semi-permeable to sodium chloride, and 

 so preventing the toxic effect of this salt upon 

 the embryo within. 



But whatever the importance of the expla- 

 nation of the phenomena in the moribund 

 fruit, the physiological meaning of the as- 

 sociated colloid during its period of develop- 

 ment is certainly not of less. It is known that 

 the coagulation of casein by HCl may be 

 prevented by the association, with the casein, 

 of another, a " protective," colloid (Alex- 

 ander, 1910). On the strength of this fact, 

 Alexander has been able to throw an impor- 

 tant light on the digestibility of human, as 

 compared with bovine and certain other 

 milks. It seems not improbable that, in the 

 growing cell, such is the relation of its associ- 

 ated colloid to the tannin, thus preventing its 

 attack upon the protoplasm. This, as a 

 working theory, has a not inconsiderable ten- 

 tative value. In harmony therewith is the 

 fact that the tannin in the persimmon, as in 

 the date, always remains within the cell, the 

 tannin-idioplast, in which it originates 

 (Lloyd, 1910, 1911). 



Concerning the action of heat, which, it has 

 already been said, causes coagulation of the 

 associated colloid, Vinson, cited above, has 

 shown that too high temperatures, sufficient 

 to destroy enzymes, prevent normal ripening 

 (that is, as related to astringency), while suit- 

 able temperatures, yet fatal to protoplasm, 

 hasten it. He sees in these facts evidence of 

 the presence of enzymes. I have shown that 

 high temperatures (that of the boiling of con- 

 centrated cane-sugar solution) actually coagu- 

 late the associated colloid (1911), but without 

 the complete imprisonment within it of the 

 tannin. It seems clear from this that the time 



