272 



SCIENCE 



[N. S. Vol. XLVI. No. 1185 



A number of tests were made in which the 

 same bio-colloid was successively subjected to 

 a series of reagents with exposures of two 

 hours or more to each one in succession as 

 follows : 



Sodium Hydrate Sodium Hydrate Hydroclilorlc Acid 



MIlOO jlZ/lOO J//100 



360 300 Slight and irreg- 



ular shrinkage. 



Plates of agar 90 parts gelatine 10 parts, 

 .07 mm. in thickness swelled 1,143 per cent, 

 in 45 minutes in distilled water, then 213 



^ . HCl if . „ , ^, .on 



per cent, m ^^ -— - m 2 hours, then 4.30 per 



cent, in KC1(M/100) in the next 4 hours, 

 after which it stood in the acidified potassium 

 chloride solution without measurable change 

 for 11 hours. The replacement of this solu- 

 tion by a hundredth molar sodiuxn-hydrate 

 solution was followed by an increased imbibi- 

 tion equivalent to 643 per cent, of the original 

 plate in two hours, at the end of which period 

 it had swelled altogether about 2,400 per cent, 

 of its original thickness. 



A similar plate swelled initially 3,357 per 

 cent, in 14 hours in water, then shrank about 

 300 per cent, in a hundredth molar acidified 

 potassium chloride solution in 11 hours, after 

 which it swelled about the same amount in 

 hundredth molar hydrate. 



Some very striking results were obtained by 

 plates .12 m m. thick of 90 parts agar and 10 

 parts bean protein. A trio of samples swelled 

 1,416.5 per cent, in 4 hours in distilled water, 

 then shrank 208 per cent, in hundredth molar 

 acidified potassium chloride in 3.5 hours, then 

 swelled 643 per cent, in hundred molar sodium 

 hydrate in 13 hours and 1,250 per cent, in 

 distilled water in 14 hours. At the end of 

 this time a total increase of about a hundred 

 per cent, in hundredth molar hydrochloric acid 

 took place. A second trio of same material 

 swelled about 400 per cent, in less than an hour 

 in water, then 200 per cent, in 3 hours in hun- 

 dredth molar acidified potassium chloride so- 

 lution, then 750 per cent, in 3.5 hours in 

 hundredth molar sodium hydrate, 1,583 per 

 cent, in water in 10 hours. After this total 

 imbibition of about 2,500 per cent, had been 



reached immersion in hundredth molar acidi- 

 fied potassium chloride for 3 hours produced a 

 dehydration of only 167 per cent., not all of 

 which was regained when the acidified salt so- 

 lution was replaced with water. 



These two series serve to illustrate changes 

 in imbibition capacity which might take place 

 in the protoplast. It would be highly unwise 

 to generalize upon the basis of the meager re- 

 sults available, yet the records described sug- 

 gest certain reasonable assumptions. Among 

 those may be included the inference that after 

 a plate of bio-colloid is in a swelling stage 

 the addition of an acidified salt solution checks 

 the rate of swelling if the total amoimt is still 

 below that possible in the solution. If the 

 swelling is already beyond the total possible 

 in the acidified salt solution some dehydration 

 occurs, but by no means enough to reduce the 

 swelling to the acidified salt total. Dehydra- 

 tion effects from hydrochloric or citric acid 

 were very slight. The application of alkalies 

 in advanced stages of swelling after acidified 

 salt solutions seemed to increase swelling be- 

 yond the total possible in a simple immersion 

 in alkali. 



Analyses of modifications of growth rates 

 must therefore take into account not the 

 simple total effect of any solution upon the col- 

 loids of the enlarging protoplast, but upon 

 these bodies as already modified by previously 

 acting solutions. 



The chief interest in all of the experimenta- 

 tion on imbibition described in this and in 

 previous papers has been directed to various 

 effects simulating growth by acids, alkalies, 

 salts and combinations upon bio-colloids as 

 illustrated by the mixtures described. The 

 differential action which might ensue from the 

 addition or subtraction of a nitrogenous com- 

 pound from the carbohydrate body of proto- 

 plasts in special tracts, changing the imbibition 

 capacity of chromosomes, of spindles or cell 

 plates, etc., may well play an important part 

 in the mechanics of mitosis and cell division. 

 D. T. MacDougal, 

 H. A. Spoehr, 



Deseet Laboratory, 



Tucson, Arizona, 



June 4, 1917 



