Rates of oxidation and reduction of blood 173 



The practical difficulties about a method which sounds so simple 

 are considerable. As compared with a haemoglobin solution great 

 trouble is caused in the case of blood by frothing, which may easily 

 become sufficiently serious to vitiate the experiment. 



On the whole the best method was arrived at by taking advantage 

 of the tendency to froth. It consisted in allowing nitrogen to bubble 

 at a uniform rate through a tube 9 mm. in bore of the shape 

 shown in the figure. The tube was placed in a bath at a known 

 temperature. The gas entered at A. Each bubble, as it arrived 

 at the surface of the blood B, formed a film which was pushed up 

 the tube until at last it was broken by a spiral of wire greased with 

 vaseline. 



FIG. 91. A, rubber tube leading from gasometer attached to glass tube of capillary bore, 

 the volume of which up to the tap should be '1 '15 c.c. B, bubble of gas about 

 to form a film. C, mark on glass bath for purpose of levelling the apparatus. I), 

 surface of water in bath at 37 C. E, spiral of greased copper wire. 



The films were formed and driven up the tube with quite 

 remarkable regularity. It seemed that in spite of a certain degree of 

 empiricism the method did give reliable comparisons between one 

 sample of blood and the next. It is a matter for regret that the 

 method, unlike the dissociation curve, is not one which has any 

 absolute physical significance. The validity of the comparisons made 

 depends upon their all being done in the same tube under the same 

 conditions of inclination, &c. If experiments of this character could 

 be carried out under conditions which could be reproduced at will, 

 they would be the source of the most illuminating information. 



At suitable intervals of time the bubbling was stopped, a little 

 blood was abstracted for analysis by taking off the tubing at A and 

 using the portion of the tube below the tap as an automatic pipette. 



