356 LEWIS V. HEILBRUNN. 



agglutination, and sometimes "blister" formation. Its power 

 of producing membrane elevation is, therefore, chiefly due to 

 the process of "sensitization," the real nature of which has al- 

 ready been considered. The agglutinating effect is due to the 

 presence of free hydrochloric acid. Robertson prepares oocytin 

 by precipitating blood serum with BaClo dissolving the precipitate 

 in n/io HC1, reprecipitating with acetone, and then redissolving 

 in n/io HC1. The result of this process can not be other than 

 the isolation of a protein combined with HC1, for we know both 

 BaCl 2 and acetone as protein precipitants. 1 And, although 

 Robertson exactly neutralizes his final product with NaOH, 

 he, of course, does not neutralize the combined acid which has 

 no action on the color of the indicator. On dilution, the com- 

 bined acid is split off. Thus Robertson finds that a dilution of 

 one part in two hundred is necessary in order that the oocytin 

 become effective. Dilute HC1 will produce agglutination in the 

 same way as oocytin. 



Higher Fatty Acids. Loeb 2 finds that very dilute solutions 

 of heptoic, octoic, nonoic, and caproic acids produce membrane 

 elevation in eggs exposed to them. As Forch 3 and others have 

 shown, the higher fatty acids lower surface tension markedly, 

 even when present in great dilution. The readiness with which 

 a fatty acid lowers surface tension is found to be in direct relation 

 to the number of carbon atoms it contains. 



Lower Fatty Acids. Mineral Acids. There remain to be con- 

 sidered only those cases in which membrane elevation occurs 

 after a return to sea-water. In all of these cases, the solutions 

 in which the eggs are first placed are acidified. All of the acids 

 used lower surface tension and their effectiveness is in direct 

 measure to the readiness with which they do so. The lower fatty 

 acids, formic, acetic, propionic, butyric, and caproic, lower sur- 

 face tension markedly in solution, and this power increases as 

 we ascend in the series. 4 Similarly, the effectiveness in producing 

 membrane elevation increases with the number of carbon atoms. 



1 Mann ("Physiological Histology," p. 102) finds acetone a precipitant of serum 

 globulin and other proteins. 



2 Loeb, "Chemische Entwicklungserregung," 1909, p. no. 



3 Forch, Wied. Ann., LXVIIL, 801 (1898). 



4 Forch, loc. cii. 



