Vol.. 7, 1921 
CHEMISTRY: D. D. VAN SLYKE 
229 
was made to determine whether or not this 1 : 1 ration was actually realized, 
but XXY individuals were found without difficulty in the material put 
up for cytological study. 
Discussion. — The evidence is not yet sufficient to indicate the exact 
relationship between the chromosomes of the two species considered here, 
but it does indicate that either the chromosomal resemblances are merely 
superficial or that the sex determining element (gene? or genes?) has been 
transferred from one chromosome pair to another. A comparison of the 
sex-linked mutant characters in the two species ought to throw some 
light on this question. It has not done so up to the present, however, for 
although we have obtained 27 such characters in willistoni they show so 
little resemblance to any in melanogaster (either sex-linked or non sex- 
linked) that they give no clue to chromosomal relationships. 
The observed frequency of secondary non-disjunction in willistoni 
(average 1.7%) was less 5 than that found by Bridges in melanogaster 
(4.3%). There is no indication at present as to why this should be the 
case unless the size of the sex chromosomes be considered a factor. 
1 The "m" chromosomes are often difficult to detect. They may be lacking 
entirely in willistoni. 
2 D. willistoni Sturtevant (D. pallida Williston). 
3 Dr. Bridges kindly informs us that he has subsequently verified this conclusion. 
4 We are indebted to Dr. Jose Nonidez for making the drawings for figures 3-10. 
5 Line D may possibly be an exception but the small numbers make this doubtful. 
« Bridges, C. B., Genetics, 1, 1916 (16-52, 107-163). 
7 Metz, C. W., /. Exp. Zool, 21, 1916 (213-276). 
AN APPARATUS FOR DETERMINATION OF THE GASES IN 
BLOOD AND OTHER SOLUTIONS 
By Donald D. Van Si,yk3 
Hospital of the Rockefeller Institute, New York 
Communicated July 5, 1921 
The apparatus consists of a pipette with the upper stem closed by a 
stopcock, the lower connected with a glass tube. The latter descends 
800 mm., then turns at a right angle to connect with a levelling bulb and a 
mercury manometer open at the upper end. The pipette is calibrated at 
two points to hold a and A cc, respectively, as shown in the figure. 
For an analysis the pipette is filled with mercury. The solution to be 
analyzed, followed by the reagents to free the gases (e.g., acid for C0 2 in 
carbonates) is admitted with slight negative pressure through the upper 
cock, displacing mercury in the pipette. A Toricellian vacuum is created 
by lowering the levelling bulb, and the meniscus of the mercury in the 
