TRANSACTIONS OF SECTION I. YD) 
TUESDAY, AUGUST 23. 
The following Papers were read :— 
1. Changes in the Reaction of Milk under Different Conditions. 
By Professor T. H. Mizroy, M.D. 
The reaction of the milk was determined by estimating the hydrogen-ion 
concentration by the electrometric method. ‘When hydrogen is passed through 
fresh milk the H concentration is lowered by a removal of carbonic acid. This 
may be avoided either by passing the milk into an electrode already charged with 
hydrogen and then shaking the milk in the vessel until it is saturated with the 
gas, or better by passing the hydrogen through a series of tubes containing milk 
before passing into the electrode containing the same milk. When this is done 
the H concentration of fresh milk is found to vary from about 1:58 x 10-7 N 
normal to 2:°24x10-’ N. Greater acidities than the latter are due to commencing 
acid fermentation of the milk. When milk is heated for about an hour at a 
temperature a little below boiling-point, evaporation being prevented, the milk 
when cooled to room temperature shows a slightly higher H concentration than 
the same milk examined fresh. There is also a greater constancy in the concen- 
tration when one compares a large number of specimens. Such heated milk does 
not undergo coagulation with rennin unless its acidity is raised by the addition 
of weak acid or by the addition of calcium chloride. The addition of calcium 
chloride raises the H concentration and produces coagulability of the milk more 
readily, that is at a lower H concentration, than when weak acids have been 
added. When potassium oxalate is added to milk, in just sufficient quantity to 
prevent coagulation, the H concentration is lowered below the level of that 
observed in ordinary coagulable milk. If one now estimates the H_ concen- 
tration after the addition of just sufficient CaCl, to produce clotting, it is found 
to be within the H concentration limits of ordinary coagulable milk. The 
addition of oxalic acid to oxalate milk does not produce true coagulation, 
2. Variations in the Hydrogen-Ton Concentrations of the Blood. 
By Professor T. H. Minroy, M.D. 
The.concentration of the hydrogen-ions in the blood can be most satisfactorily 
determined by the electrometric method. There are certain difficulties entailed 
in the method as employed for blood, owing to the fact that the blood is rich in 
oxygen and in carbonic acid. The former gas leads to a depolarisation of the 
hydrogen plate, and so the estimation can only be made after complete reduction 
of the blood, while the latter gas must be prevented from leaving the blood, as 
the variations in the hydrogen-ion concentration are mainly due to changes in 
the carbonic acid content of the blood. 
When the necessary precautions are taken to avoid these fallacies the method 
is sufficiently accurate to enable one to determine the variations due to altera- 
“tions in respiration if these alterations be of a sufficiently marked character. 
It may readily be shown that the concentration falls after a period of pro- 
longed pulmonary ventilation and rises again during the period of apnea. If 
the period of ventilation with air be succeeded by a short period with 10 per 
cent. carbonic acid in air, then the usual fall in concentration does not occur, 
and so there is no resultant apnoea. 
The fall that is produced after ventilation with rich oxygen-holding mixtures 
is of the same degree as that observed after inflation with air. To show the 
degree of the changes in H concentration an example may be given. 
Before ventilation the hydrogen-ion concentration of the blood was 
3715 x 10-7 N, while after fifteen minutes’ ventilation with air, followed by two 
minutes and fifteen seconds with oxygen, the concentration was *1995 x 10-7N. 
An apneic pause of three minutes ten seconds’ duration followed the ventilation 
period, and at the close of this the concentration had risen to °3548 x 10-7 N. 
Ten minutes later when breathing was again of normal character the concen- 
tration had risen to -3890 x 10-7N. 
In certain rare cases ventilation does not produce the usual fall, and when 
