W. J. V. OSTERHOUT 169 



by the addition of ether may be freed from ether by a current of air^ 

 and does not decolorize rapidly until it has stood for some time. 

 Blood which has been carefully dried to a jelly-like mass may be 

 kept in this condition; it dissolves readily on the addition of water. 

 But if dried to a hard, brittle mass it does not readily dissolve. 



Under favorable conditions blood containing certain organisms,^ 

 (such as bacteria, or young Limulus in the trilobite stage) is quickly 

 decolorized (in some cases within 2 minutes) and the time required 

 for decolorization is remarkably constant.^ 



When the normal rate of oxygen consumption has been established 

 by repeated determinations, reagents may be added and changes in 

 the rate may be determined. In this way the relative rate under the 

 influence of the reagent may be ascertained without knowing the 

 absolute amounts of oxygen consumed in either case. 



A variety of other substances, such as indigo-carmine, methylene 

 blue, malachite green, etc., are also reduced and it is possible that 

 some of them may prove more useful than Limulus blood. Experi- 

 ments on this subject are being continued. 



SUMMARY. 



The blood of the horseshoe crab {Limulus) absorbs oxygen and 

 turns blue when shaken in air. In the presence of certain organisms 

 which consume oxygen it is quickly decolorized. By measuring 

 the time required for the change of color the rate of consumption 

 of oxygen may be determined. 



^ The air should be filtered or washed to remove bacteria before entering the 

 blood. 



^The salt content must be adjusted to the needs of the organism; it may be 

 quickly ascertained by titration. 



^The normal rate is sometimes irregular, due to factors not fully under- 

 stood. In these cases the results are rejected. The disturbing factors require 

 further study. 



