354 LEWIS V. HEILBRUNN. 



process as Moore 1 and Robertson 2 would have us believe when 

 they suppose that it is similar to the process of mordanting 

 before dyeing. An experiment of Moore's seems to show that 

 my explanation is correct. Upon placing eggs in 3/8 SrClo, and 

 then removing directly into sea-water, sensitization occurs, but 

 if the eggs are first washed in NaCl before being placed in sea- 

 water, the effect of the SrCl 2 disappears. Evidently the washing 

 away of the SrCl 2 prevents its reaction with sea-water. 



The effect of serum alone is very slight. Of nine samples of 

 ox-sera tried by Robertson, only one was effective upon sensitized 

 eggs. I attribute the effect of blood serum to two causes. In 

 the first place, before dilution with sea-water the salt content of 

 the "isotonic" serum is almost wholly NaCl, together with a 

 small amount of KC1. The effect of isotonic NaCl and KC1 

 solutions has already been discussed. Secondly, blood serum 

 contains considerable amounts both of oxygen and of carbon 

 dioxide. The total volume of these gases contained in blood 

 varies greatly. On the average, arterial blood possesses about 

 20 vols. per cent, of oxygen and 40 vols. per cent, of carbon 

 dioxide, whereas venous blood contains approximately 7 volumes 

 per cent, of oxygen and 50 volumes per cent, of carbon dioxide. 3 

 Blood serum is richer in carbon dioxide than the blood itself. 4 

 Thus the serum used by Loeb to produce membrane elevation 

 must contain from 5 to 25 volumes per cent, of carbon dioxide 

 in addition to a lesser amount of oxygen. 



No doubt some of this CO 2 is loosely combined, but even in 

 this case it would exert a dissociation pressure which would 

 increase the amount present in solution. Using ox-blood ob- 

 tained from a slaughter-house, Robertson found a difference in 

 the serum obtained from dark and that obtained from light 

 blood, the former being in all cases more effective. He is at a 

 loss for an explanation, but suggests that the dark blood was 

 obtained from animals deprived of water for some time. Prob- 

 ably the dark color of the more effective blood is associated with 

 the presence of a higher per cent, of CO 2 . The action of CO 2 



1 A. R. Moore, Univ. of Cal. Pub'. (Physiology), IV., 91 (1912). 



2 T. B. Robertson, loc. cit., p. 345. 



3 See Oppenheimer's "Handbuch der Biochemie," IV. (T). 



4 Hammersten, "Physiological Chemistry," 6th Amer. edition, p. 804. 



