September 14, 1917] 



SCIENCE 



271 



The swelling increases -within the range of 

 concentration of potassium nitrate used, and 

 appears to decrease slightly within similar 

 concentrations of potassium chloride, and is 

 checked to a greater extent by calcium chlo- 

 ride, although the last named solution would 

 have a slightly all^aline reaction due to the 

 hydrolysis of the salt. 



The eilect of salts alone on the bio-col- 

 loid in which gelatine forms the nitrogenous 

 constituent is shown by the following meas- 

 urements of the swelling of a series of dried 

 plates of 90 parts agar and 10 of gelatine, 

 .22 mm. in thickness: 



The next step to be taken was one in which 

 the eifect of the universally present salts were 

 tested in various concentrations in connection 

 with conditions of acidity and of deacidity. 



As an example of such tests the results ob- 

 tained by a study of the action of dried plates 

 of a mixture of 90 parts agar and 10 parts 

 bean protein are given below: 



769.2 



Calcium Chloride 



Hydrochloric Add 



-V/100 



538.5 



It is apparent from these results that acid- 

 ity decreases the amount of imbibition in the 

 presence of the salts tested. 



A few tests made to determine the limits of 

 imbibition in concentrated solutions revealed 

 the fact that dried plates of 90 parts agar and 



10 parts of bean protein swelled 57G.9 per 

 cent, in a saturated solution of potassium 

 nitrate which has an osmotic coeiEclent of 

 about 60 atmospheres. The same material 

 swelled 730.9 per cent, in a solution of 50 g. 

 of calcium nitrate in 100 cc. of water (2-molar 

 solution) which has an osmotic coefficient of 

 about 44 atmospheres. A swelling of 100 per 

 cent, was shown in a 3-molar solution of 

 calcium chloride and if hundredth molar 

 hydrochloric acid was added the swelling was 

 increased to as much as 200 per cent. These 

 facts illustrate very forcibly the possibilities 

 of imbibitional absorption against osmotic 

 action. The significance of such action in 

 parasitism and nutritive couples has been 

 discussed elsewhere.^ 



All tests in which the samples of colloid 

 are presented to the action of the reagent in a 

 neutral and dried condition are of course 

 widely different in hydratation conditions from 

 those prevalent in the protoplast. The col- 

 loids of the living material are continuously 

 subject to interaction and to modifications 

 resulting from the action of salts, acids, al- 

 kalies and their combinations. 



A few tests in which plates of bio-colloid 

 swelling from the action of one solution 

 are subjected to another have already been 

 described. The possibilities presented, how- 

 ever, are such as to justify the minutest exam- 

 ination. 



In one series dried plates of 90 parts agar 

 and 10 parts bean protein were first subjected 

 to the action of alkali, to hydrochloric acid 

 and to citric acid separately for eighteen 

 hours, at the end of which time their full im- 

 bibitional capacity had been reached under 

 the separate influence of each of these rea- 

 gents. The solutions were then pipetted ofF 

 and a second reagent introduced. The initial 

 and the secondary action are indicated below. 



First Swelling 



Hydrochloric Acid .V/100 Citric Acid -V/IOO Sodium Hydrate MIlOO 



300 9o 402% 400% 



2 See MacDougal, D. T., ' ' The Beginning and 

 Physical Basis of Parasitism," Plant World, 1917 

 in press. 



