636 



SCIENCE 



[N. S. Vol. LIV. No. 1408. 



lu order to increase the number of test 

 matings, the males, 4,595 and 4,388, were 

 mated with females which were merely heter- 

 ozygous for angora coat, animals which were 

 themselves short-haired but which had one 

 parent an angora. Therefore only half the 

 gametes of these females, viz., those which 

 bore angora, would be useful in the test ma- 

 tings. Accordingly half the total young from 

 such matings have been deducted before en- 

 tering the totals in Table I., and of course 

 the deductions have been made from the 

 short-haired classes, equal numbers being de- 

 ducted from the English and the non-English 

 groups. Apparently male 4,595 gives a lower 

 percentage of cross-overs than male 4,388, 

 and the female double heterozygotes give a 

 lower percentage than either male, but the 

 totals are not large enough to give much 

 weight to these ideas. The average result for 

 all test matings is a cross-over percentage of 

 9.0 zt 1.5, which means lirLkage of strength 

 82 =t 3, on a scale of 100. This certainly is 

 a significant result, which indicates that the 

 characters English and angora have their 

 genes in the same chromosome. 



W. E. Castle 

 BussET Institution, 

 December 1, 1921 



THE HYDROGEN-ION CONCENTRATION OF 



CULTURES OF CONNECTIVE TISSUE 



FROM CHICK EMBRYOS 



In view of the fact that tissue cultures in 

 Locke-Lewis solution were to be used in observ- 

 ing the behavior of living cells when exposed 

 to bacteria and other foreign substances, it be- 

 came necessary to determine the optimum and 

 the final hydrogen-ion concentration of the 

 cultures themselves. For the purpose several 

 hundred cultures of connective tissue of chick 

 embryos were prepared, in Locke-Lewis solu- 

 tion with varying hydrogen-ion concentrations 

 and containing different amounts of dextrose. 



The normal solution was composed of 85 c.c. 

 of Locke's solution (NaCl 0.9 per cent, plus 

 KCl 0.042 per cent, plus CaCl^ 0.025 per cent, 

 plus ]SraHC03 0.02 per cent.), together with 

 15 c.c. of chicken bouillon and 0.5 per cent, 

 dextrose. This solution has a hydrogen-ion 



concentration between 6.6 and 7, depending 

 upon that of each lot of bouillon. For the ex- 

 periments the hydrogen-ion concentration was 

 varied from pH 4 to pH 9.2 with an increment 

 of 0.2, and the amount of dextrose was varied 

 from 5 per cent, to none at all. 



The hydrogen-ion concentration of the cul- 

 tures explanted into these solutions was deter- 

 mined at different stages of their growth, 

 namely, when they failed to grow, when they 

 exhibited extensive and healthy growth, and 

 when they had degenerated after vigorous 

 growth. This determination was made by a 

 colorimetric method devised by Felton (1921) 

 by means of which it is possible to test the 

 small hanging drop of a culture. 



Early in the investigation it was discovered 

 that not all kinds of coverglasses were suitable 

 for the experiments because of the change in 

 hydrogen-ion concentration exhibited by con- 

 trol drops (without explant) when incubated 

 upon this glass. It became necessary, there- 

 fore, to select coverglasses on which the con- 

 trol drop remained constant when incubated for 

 a period of three weeks. 



When cultures of embryonic chick tissue 

 were prepared on reliable coverslips, those ex- 

 planted into a medium with a hydrogen-ion 

 concentration of 4 to 5.5 seldom showed any 

 growth; those in a medium pH 5.5 exhibited 

 growth in a few instances; while those in 

 media having a hydrogen-ion concentration 

 from pH 6 to pH 9 usually showed abundant 

 growth. Approximately one hundred cultures 

 were explanted into solutions pH 6, 7, 8, and 

 9. The percentage of growth which occurred 

 in these cultures was respectively 71, 93, 89 

 and 81, while that of the normal cultures 

 (pH 6.6-7) was 90 per cent. The optimum 

 hydrogen-ion concentration seemed to be about 

 pH7. 



When the hydrogen-ion concentration of 

 these cultures was tested at different stages of 

 their growth, it was noted that while it dif- 

 fered markedly, this was dependent much more 

 upon the state of the culture at the time the 

 test was made, and also upon the amount of 

 dextrose in the medium, than upon the initial 

 hydrogen-ion concentration of the medium. 



