At the present stage of our knowledge, the rhythm may perhaps be considered as an expression of a sort of temporary "senescence," for which is provided an internal, automatically working, antidote in the form of endomixis. But, if one considers this as a "senescence "-phenomenon and endomixis a "rejuvenation "-phenomenon, then it is equally permissible so to consider the momentary fluctuating periods of anabolic and catabolic ascendency in the metabolism of the cell. But I would point out that it is a case of trying to force new wine into old bottles in order to save an idea, and that this line of reasoning, pushed a little farther, approaches perilously near a reductio ad absurdum. One certainly must grant that the prevalent idea of "senescence" in infusoria is far removed from this subtle, automatically eliminated type which rhythms may indicate.

The work at Yale in the past has been to determine whether conjugation is a necessary factor in the life of infusoria; and we believe that 5250 generations without conjugation is strong evidence in the negative. But, obviously, because conjugation is not necessary in the life of Paramacium under favorable environmental conditions, it does not follow that conjugation is not necessary under other conditions, or that it does not have a "rejuvenating" function. There is nothing mutually exclusive in the fact that conjugation is not necessary and the idea that conjugation has a dynamic function when it occurs. In fact we have always leaned toward and definitely stated the view that conjugation probably has a dynamic function, which is important when the organisms are subjected to unfavorable conditions. Calkins has secured some evidence which indicates that, after conjugation, all the processes of the cell including reproduction proceed with greater vigor; and thus he substantiates the view of Bütschli, Maupas, Hertwig, and others. Jennings, on the other hand, definitely states that there is no evidence from his work that conjugation in the infusoria increases the reproductive power of, or rejuvenates, the organism physiologically in any way and puts all the emphasis on the side of variation and heredity.

However, since the cytological phenomena of conjugation, with the exception of syncaryon formation, are so similar in their broad features with those of endomixis, and since accelerated vital activities including reproduction do follow endomixis, it seems reasonable to believe that accelerated vital phenomena follow conjugation-that is, that both processes, broadly speaking, "rejuvenate" the organism physiologically. Both processes afford opportunity for a rearrangement of the molecular constitution of the cell, conjugation affording amphimixis and endomixis affording endomixis.

To recent contentions that our conclusions were wrong, in regard to conjugation not being a necessity for the continued reproduction of infusoria, we would reply that endomixis is not conjugation; and no one had any other phenomenon than conjugation, involving syncaryon formation, in mind until the discovery of endomixis, in which a syncaryon is not formed. To say that endomixis fills essentially the same rôle as conjugation in the infusorian life-history is to beg the entire question. In a word, the whole aspect of the problem of senescence and rejuvenescence in protozoa has changed with our knowledge of endomixis. The question is now not whether conjugation is necessary for it is not but whether endomixis is necessary. If endomixis is necessary, as it may well be, and if one feels justified in considering the physiological phenomena which are synchronous with the start of endomixis as evidence of "senescence" and those synchronous with the end of endomixis as indicating "rejuvenation" then, this is a radically new phase of the old idea of protoplasmic senescence and rejuvenescence in the in

THE CHEMICAL CONSTITUTION OF STARCH

A review

ARTHUR W. THOMAS

The size and configuration of the starch molecule have been the subject of much chemical research since about 1836, when Payen1 announced the chemical composition to be C6H1005. This is the empirical formula generally accepted at the present time. The real molecular structure is known to be many times this empirical unit, however. The highly colloidal nature of starch, the ease with which it can be removed from its solutions by merely forcing them through porous earthenware, and the extremely small influence which it exerts on the freezing point of its solvent, are facts that indicate a high degree of molecular complexity, which probably approaches that of the proteins.

The (C6H10O5), structure indicates that starch is an anhydride condensation product of glucose or maltose. This view is borne out by the fact that hydrolysis by acid or diastase yields glucose or maltose, respectively, as the end products. The contributions to our knowledge of the molecular weight have all, or nearly all, depended upon the study of the hydrolysis of starch by infusions of malt, a type of study which has naturally been fostered by the great fermentation industries.

In 1860 Musculus noted that it was difficult, in fact quite impossible, completely to hydrolyze starch to maltose by means of malt. After much experimenting he announced, in 1878 (Musculus and Grueber), his view that starch must be a polysaccharide of a molecular size indicated by the formula (C12H20O10) 5-6. In 1879 O'Sullivan announced that the starch molecule is as large as the molecular size (C12H20O10) 6, thus corroborating the work of Musculus.

Herzfeld, while not contributing directly to the knowledge of the size of the starch molecule, started a new line of thought, in which he pointed out that the hydrolysis progressed through a series of dextrins of diminishing complexity before, or in the course of, the conversion of starch to sugar, i. e., starch, to soluble starch, to erythrodextrin, to achroodextrin, to maltodextrin, finally to maltose. To maltodextrin he assigned the formula C18H36016The discovery of maltodextrin was quite a significant step, for all subsequent work has depended on the study of just such substances -substances which combine the properties of sugar and of dextrin.

Brown and Heron found that the hydrolysis of starch by malt stopped when four fifths of its weight of maltose was formed, the remaining one fifth consisting of a dextrin. They accepted the theory of Musculus and Grueber, and of Herzfeld, that starch was hydrolyzed in successive steps to dextrin and to sugar. From their experiments with malt diastase they concluded, most naturally, that the starch molecule must be at least five times the size of the residual dextrin, and proposed (C12H20O10) 10 as the formula for starch, the simplest dextrin molecule being thought to be (C12H20O010)2.

In 1885, Brown and Morris' reported that a dextrin was always present as one of the hydrolytic products of starch, which, while not identical with the maltodextrin of Herzfeld, bore a resemblance to it. They assigned to this compound the formula (C12H20O10) 2 C12H22O11. Inasmuch as this dextrin was difficult to hydrolyze they gave starch the formula 5 (C12H20O10) 3, in order to make it agree with the principles evolved from their earlier work. The (C12H20O10)3 group was called amylin, the starch molecule consisting of four such groups arranged symmetrically about a fifth. Upon hydrolysis an amylin group was thought to split off as maltodextrin, leaving the other four as a more complex dextrin, the maltodextrin in turn splitting directly into maltose.

Brown and Morris determined the molecular weight of amylin Herzfeld: Berichte, 1879, xii, p. 2120.

6 Brown and Heron: Ann. Chem., 1879, cxcix, p. 165.

7 Brown and Morris: Ann. Chem., 1885, ccxxxi, p. 72.

8 Brown and Morris: Jour. Chem. Soc., 1889, lv, p. 96; Berichte, 1891, xxiv,

P. 723.

by means of its depression of the freezing point of water. Their experimental figure for the molecular weight was 6221, which agreed most closely with the formula (C12H20O10) 20, the molecular weight of which is 6480. They adhered to their theory that starch was composed of five amylin groups and represented the hydrolysis by these equations:

First, (C12H20O10) 20 + H2O → C12H22O11 (C12H20O10) 19
Amylin
Last, (C12H20O10) 20 + 19H2O→ (C12H22O11) 19. C12H20010

Maltodextrin

Brown and Morris concluded, from the results of their later work, that the maltodextrins split into smaller substances of varied composition. Two different maltodextrins were isolated by the authors, one with the formula (C12H20O10) 2. C12H22O11 (maltodextrin) and another with the formula (C12H20O10) 6.C12H22O11 (amylodextrin).

Scheibler and Mittlemeier, in 1890, discussed the hydrolytic products of starch and dextrin. One noteworthy feature of their paper was the preparation of the hydrazone of a commercial dextrin which, upon analysis, was found to have a composition indicated by the formula, C96H162O80N2HC6H5. This corresponds with (C6H10O5) 16, which is somewhat similar to the amylodextrin reported by Brown and Morris.

Lintner and Duell1o claimed that, in its hydrolysis, the complex starch molecule split first into amylodextrin (better known at the present time as soluble starch), and that this soluble starch then broke down into three molecules of erythrodextrin, which in turn split into three molecules of achroodextrin, the latter splitting into iso-maltose, iso-maltose changing to maltose. They determined the molecular weight of these substances by means of the freezing

point method of Raoult, with the following results:

In 1897 a formula only one quarter as great as that of Lintner