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making of the plates which furnished the sections used in the swelling tests. It is seen therefore that the swelling of agar shows a maximum in a hydrogen ion concentration greater than its own as well as in the hydroxide solution at PH II.
The above results are to be applied in correction of statements made in many previous publications as to the retarding action of the hydrogen ion on the swelling of pentosans. This mistaken conclusion has been most recently made in the Report of the Department of Botanical Research of the Carnegie Institution of Washington for 1920, pp. 54 and 55, in which it is said that "The pentosans are weak acids and in general their hydration capacity is lessened by hydrogen ions. Hydroxyl ions and compounds containing the amino-groups, such as may be in solutions of phenylalanin, alanin, asparagin and glycocoll, may exert an effect by which hydration capacity is increased above that in pure water. Mucilages derived from various sources show some differences in reactions to the solutions named while conforming to the generalizations given. Their hydration is but little affected by the presence of the common sugars in the water of suspension or dispersion."
Some differences in the reactions of the different plant mucilages to the action of hydrogen and hydroxyl ions might reasonably be attributed to the varying acidity of these substances. Thus commercial acacia gum (gum arabic) and purified cherry gum in a 1 per cent, solution have a РH value of 5.1, which is not far from that of a sample of "Bacto" gelatine in an 8 per cent. solution. The mucilage of Opuntia, which is taken to form an actual part of the plasmatic mass in the cells of this cactus has a Рн value of 5.8 as determined by the indicator method.
The data presented in the foregoing table show that the chlorides of the four metals at 0.0001 M with a PH value ranging from 5.6 to 6, cause an excessive hydration, which in terms of water as 100, would be CaCl2, 110; MgCl2, 116; KCl, 113; NaCl, 150. At 0.001 M KCl which has a РH value of 5.8 as compared with a value of 5.7 at 0.0001 M also causes an excessive hydration. Marked differences are shown by the sections from the two plates in solutions in this concentration, the swelling of one in the sodium being excessive and that of the other lessened. It is to be noted that in the
hydroxides at 0.01 N the metals exert a lessening effect on hydration in a series which runs Ca, K, Na with the least swelling in the calcium. In the chlorides at 0.01 M the series runs Ca, K, Na, a coincidence strongly suggestive of the specific action of the bases or cations, which has eluded many experimenters.
Sections of the agar Plate B were also swelled in nitrates and sulfates of sodium and potassium at 14-15° C. with increases as noted in Table II.
It is to be seen that swelling in the sulfates does not exceed the amount possible in water even in the dilute solution, while at 0.0001 M the swelling in the nitrates of both sodium and potassium is in excess of that possible in water.
The effect of the salts on gelatine is one which has received attention at the hands of many investigators, but the recently published results of Loeb on the action of these substances at the low concentrations which may be of biological interest are the most decisive yet available. However, it was deemed important to carry out swellings of sections of this substance by the auxographic method in order to secure data strictly comparable with those obtained from the tests with agar. The gelatine was of a sample which, made up in an 8 per cent. solution, had a РH value of 5.2 Sections 0.27 mm. in thickness were swelled at 14-15° C. and increases were noted in Table III.
The hydration of gelatine as illustrated by the action of the HCI is increased by H or OH ions, the effect rising with the departure from the isoelectric point. Thus the swelling in the acid at o0.0001 M Ph value of 4.2 is scarcely more than in water, while at 0.01 M with a Ph value of 2.01 the swelling is over four times as great as Loeb, J., "The Action of Salts in Low Concentrations," Jour. Gen. Physiol., 3: 391, 1921.
in water alone. The swelling in KCl at 0.0001 M with a PH value of 5.7 is not much greater than in water, and the accelerating effect does not rise so rapidly as in the acid solution, the swelling at 0.001 M with a PH value of 5.8 being not much more than double that in water. Still another effect of interest is that of the calcium chloride solutions, which induce a maximum swelling at 0.001 M but depress hydration as the concentration rises, and as it falls away from this point.
The chief interest in all of the foregoing results lies in their possible use in interpretation of the action of living matter. Varied and extensive series of tests have proved that mixtures of pentosans or mucilages and of albumin or gelatine formed a biocolloid in which many of the reactions of living and dead cell-masses to hydration agencies might be exemplified. It was therefore believed to be of importance that the action of salts upon these mixtures should be tested in connection with a measurement of their action upon living material. As has been discussed in many previous papers the behavior of a biocolloid to a hydrating solution depends in many important features upon the proportions of the two main constituents. The action of salts was therefore tested upon two types of biocolloids, one in which the pentosan agar formed the greater proportion and another in which gelatine was the dominant component. The swelling increases of two such mixtures are given in Table IV.
It is notable that in the agar-gelatine mixture the effect of the potassium chloride is essentially identical with that produced on agar alone, except that the limiting effect at the higher concentration is less marked, being at 0.01 M but little short of the swelling in water. Sensitiveness to hydrogen ion concentration as shown in reactions to the acid was much more marked than in the agar
alone, and the swelling even in the greatest attenuation of the acid. was much less than in water. The limiting effect of the calcium chloride was also very marked.
HYDRATION OF MIXTURES OF AGAR 3 PARTS, GELATINE 2 PARTS at 14° C. Plates 0.18 mm. in thickness; swelling of sections given in thickness and in volume.
HYDRATION OF MIXTURES OF GELATINE 3 PArts, Agar 2 Parts at 14° C. Plates 0.18 to 0.19 mm. in thickness; swellings given in thickness and in volume.
The gelatine-agar mixture being a dominantly albuminous mixture, swelling in acid increased with the concentration which was carried to a PH value of 2.01. On the other hand potassium chloride exerted an effect parallel to that shown by its action on agar, the greatest swelling taking place at the lowest concentration with a PH value of 5.7, the increase being much greater than in the acid at the higher concentration.
In general the living cell masses taken from growing organs are dominantly pentosan, but some material has been examined in which the hydration reaction is that of a dominantly albuminous biocolloid. No conception of living matter in plants not including some of the all-pervading common salts is possible, and any attempt to make a complete picture of the colloidal material of the cell must
take into account the compounds of the fatty acids with the common bases, the soaps which as McBain and Salmon have recently shown may exist as both electrolytes and colloids in colloidal masses.
These soaps are an almost inevitable component of protoplasm, and some studies of their possible action in the cell will be taken up in a paper now in preparation. Preliminary to any profitable consideration of the soaps it is necessary to have some definition of the parts which salts may play in the biocolloidal machine. The measurements of swellings given in earlier papers showed that the incorporation of nutritive salts in colloidal masses lessened the hydraiton capacity. It is now apparent from the results given on the following pages that such restrictive action was due to the high concentrations employed. This however cannot be said of the amino-compounds, which used as hydrating solutions accelerated swellings, but which incorporated in colloidal masses uniformly reduced hydration capacity in whatever concentration used.
In the tests which are to be described it was planned to include the salts which are of importance in nutrition, which induce accelerated swelling in agar and agar-gelatine mixtures in implied concentrations, the calcium and sodium furthermore being used in approximately balancing proportions. These salts were first used with purified agar and hydration values as in Table VI were obtained.
HYDRATION OF AGAR AND SALTS IN SALT SOLUTIONS.
5 g. agar, 100 c.c. KC1 0.001M, 60 c.c. NaCl at 0.0001M, and 10 c.c. CaCl at 0.0001 M. Sections 0.2 mm. to 0.27 mm. in thickness swelled at 14° C.
The total swelling in the present instance is one which is equivalent to that shown by many preparations including that of agar 7 Jour. Amer. Chem. Soc., 42: 426, 1920.