STUDIES IN ARTIFICIAL PARTHENOGENESIS. 353 



however, a necessary consequence of the fact that sea-water 

 contains salts of magnesium (which constitute nearly 1/6 of the 

 total salt content). Magnesium salts are always precipitated 

 in the presence of NaOH or KOH, this reaction often being 

 employed in qualitative analysis. As a result of this precipita- 

 tion, the salts which tend most to raise the surface tension (see 

 p. 350) are precipitated and the surface tension of the sea-water 

 decreases slightly. As might be expected, alkalis are not very 

 powerful agents in producing membrane elevation. 



Blood Serum. Loeb 1 first showed that the body fluid of certain 

 annelids of the family Sipunculidse was capable of producing 

 membrane elevation even in considerable dilution. As I know 

 nothing of the chemical nature of this fluid, it is useless for me to 

 consider this case. Soon after, he found that mammalian blood 

 serum was also effective. 2 6.5 volumes of the serum are mixed 

 with one volume of 2.5 M NaCl and the resultant solution is then 

 diluted with 1-9 parts of sea-water. Loeb's results show that 

 the per cent, of eggs which "form a membrane" as a result of 

 treatment with this solution is small, in the majority of cases 

 not a single egg throws off its membrane. In order to obtain a 

 higher percentage of membrane elevation, sensitization must be 

 resorted to. This may be effected either by heating (to 3i-34) 

 or by the addition to the serum of 3/8 M BaCla or SrC^. 



First I shall consider the effects of sensitization, as I believe 

 that this process is in itself capable of producing membrane 

 elevation. The result of heating has already been considered, 

 it having been noted that a lowering of surface tension results. 

 As for the addition of BaCU or SrCU, the result must be obvious. 

 Either one of these salts causes an immediate precipitation of 

 sulphates. Loeb in fact mentions a precipitate of BaSCU in 

 the case of BaCl2, but fails to do so in the case of SrC^. Such a 

 precipitation has two effects, (i) The strontium chloride added 

 is precipitated from the solution, which then becomes more 

 dilute. (2) The sulphates of sea-water are replaced by chlorides 

 which are somewhat less effective in elevating the surface ten- 

 sion (see p. 351). Thus sensitization is not such a mysterious 



1 J. Loeb, Arch.f. d. ges. Physiol., CXVIII. (1907). 



2 J. Loeb, Arch.f. d. ges. Physiol., CXXII., 196 (1908); CXXIV., 37 (1908). 



