58 SCIENCE PROGRESS 



slower action than that o-f reductase. After many hours a tube 

 of oxyhaemoglobin kept at 40 C. is still unreduced, whereas, as 

 we have seen, certain juices at room temperature will reduce 

 twice or more of their volume of diluted blood in two to three 

 minutes. Temperatures above body temperature (40 C.) do not 

 enter into the problem in healthy animals. Since oxyhaemo- 

 globin can be slowly reduced at io°C, and even at o°C, we 

 hold that reductase is the factor operative at low temperatures 

 in the cold-blooded animals. The almost complete cessation 

 of reduction at o° C. and below is an interesting demonstration 

 in vitro of the artificial counterpart of the cessation of tissue re- 

 spiration which constitutes the condition known as " latent life." 

 In the next place, the presence of carbon dioxide in the 

 blood has been proved by Barcroft to be a factor in facilitating 

 the dissociation of oxyhaemoglobin in vitro. This is regarded 

 as a most important factor in the case of cold-blooded animals. 

 Important as this has been shown to be in laboratory experi- 

 ments, we are fully convinced that it is not the chief factor in 

 the reduction of oxyhaemoglobin even in the poikilothermic 

 animals. The factor responsible for the reduction ol oxyhaemo- 

 globin is highly insoluble ; but carbon dioxide is very soluble. 

 Similarly, traces of acid have in laboratory experiments been 

 demonstrated to facilitate the separation of oxygen from oxy- 

 haemoglobin. We do not think that this either is a factor of 

 high importance in tissue reduction. Since it is true that juice 

 kept aseptic develops acidity in autolysis, the older the juice 

 the more vigorously it ought to reduce if acid were an important 

 factor, but we have shown that the exact opposite is the case. 

 Traces of acid tend to form methaemoglobin, a pigment we have 

 never noticed in any mixture of active tissue juice and oxyhaemo- 

 globin. Again, the acids in question — for instance, lactic — are 

 soluble ; the reducing agent in press-juice is comparatively 

 insoluble. It might be noted that, in dealing with liver juice 

 and oxyhaemoglobin, we have eliminated both bile and dextrose 

 as factors in the reduction of the pigment. It may be remarked 

 that the so-called reducing power of colloids is exerted only 

 against certain pigmentary substances, and not at all against 

 oxyhaemoglobin. In other words, the "Creighton effects" have 

 no analogues in connection with the reduction of oxyhaemo- 

 globin ; for, for one thing, it is impossible to heat blood to 

 ioo° C. without its being decomposed. 



