Concentration of Carbon Dioxide of the Blood. 49 



of practically the same titer as it was at the beginning. On the 

 other hand, a considerable number of the tubes developed small 

 cracks which admitted some air. The dried antigen in these 

 tubes changed in appearance, becoming very dark and confluent. 

 This presumably oxidized lipoid was found to have lost its anti- 

 genic value entirely and also to have developed considerably more 

 anticomplementary property than the original had. 



The properties of the original preparation as an antigen were 

 about equal to those of the usual lecithin extracted from beef 

 heart. Complete fixation was obtained at a dilution of about 

 1-180,000 of the lipoid. Slight anticomplementary effect was 

 evident at a dilution of 1-7,500. This gives a ratio between 

 antigenic and anticomplementary doses of about 1-25. 



MacLean's reason for devising this method of obtaining a 

 pure lecithin was to avoid the oxidation of the unsaturated fatty 

 acid radical in the lecithin. From our observation the same 

 process, oxidation, is what ordinarily results in the loss of anti- 

 genic value; antigen can be preserved indefinitely under anaerobic 

 conditions. It is possible that this indicates that the antigenic 

 value is dependent on the presence of the unsaturated fatty acid 

 radical (oleic acid). 



30 (1405) 



Changes in the concentration of the carbon dioxide of the blood 

 following changes in the circulation through the medulla 



oblongata. 



By F. H. Pike, Helen C. Coombs and A. Baird Hastings. 



[From the Department of Physiology, Columbia University, N. Y.] 



It is desirable and even necessary, in attempting to estimate 

 the role of the afferent nerves in the regulation of the respiratory 

 movements 1 to investigate more carefully the effects upon respir- 

 atory movements of changes in the volume of blood flowing through 

 the medulla oblongata. 2 



1 Pike, F. H., and Coombs, Helen C, American Journal of Physiology, 1918, 

 vol. 45, p. 569; this journal, 1918, vol. xv., p. 55. 



2 Pike, F. H., Science, 1918, xlvii., pp. 121-122. 



