546 THE PHYSIOLOGY OF REPRODUCTION 



defined by these criteria is rather different from the conception of 

 acidosis as used by the older writers, who applied it to conditions 

 where abnormal acids such as aceto-acetic acid and oxybutyric acid 

 can be definitely identified, as, for instance, in the acidosis of diabetes 

 or of pernicious vomiting of pregnancy (see above, p. 544). In this 

 latter condition there is," as has been shown above, a greatly increased 

 excretion of ammonia in the urine for which, no doubt, the factor 

 of starvation is largely responsible, while the alveolar C0 2 shows 

 only a comparatively slight diminution, as Loosee and van Slyke l 

 point out. In normal pregnancies the observations of Hasselbalch 

 and Gamrneltoft 2 have shown that there is a slight but distinct fall in 

 the alveolar C0 2 pressure. This fall was observed in one case very 

 early in pregnancy, namely on the first occasion when menstruation 

 ceased, and gradually progressed to 30 mm. against a normal value 

 varying between 35 mm. and 43 mm. In another case the alveolar 

 C0 2 pressure before birth was 32 mm. and rose to a mean value of 

 38 mm. after birth. 



Hasselbalch also holds that the ammonia excretion is slightly 

 increased in pregnancy, although as Murlin has pointed out (see 

 above, p. 534) the argument as to the existence of an acidosis from 

 the increased ammonia excretion is open to criticism. 



There is also a distinct diminution in the C0 2 combining power 

 of the blood : the so-called " alkali reserve " of the blood. Thus 

 Siemens 3 found in normal pregnancies values of 37 c.c. to 50 c.c. C0 2 

 per 100 c.c. of plasma against values from 55 c.c. to 75 c.c. for normal 

 non-pregnant women. The toxaemias of pregnancy show the same 

 apparent paradox with reference to the alkali reserve as they do 

 with the alveolar C0 2 : the diminution of the alkali reserve in these 

 conditions is no greater than in normal pregnancies, while the 

 ammonia index gives very high figures. 



If we accept the definition of acidosis as an increased formation 

 of acid metabolites as evidenced by a fall in the alveolar C0 2 pressure, 

 then pregnancy is accompanied by an acidosis. This "acidosis" does not, 

 however, affect the reaction of the blood, which is stated to be normal. 

 It is not yet clear how this acidosis is related to the acidosis of the 

 pernicious vomiting of pregnancy, in which the main alteration of 

 the acid-base equilibrium is an increased excretion of ammonia with 

 only a slight change in the alveolar C0 2 pressure. The " acidosis " of 



1 Loosee and van Slyke, "The Toxaemias of Pregnancy," Aimer. Jour. Med. 

 Sciences, vol. cliii., 1917. 



2 Hasselbalch and Gammeltoft, " Neutralitatsregulation des graviden 

 Organismus," Bwchem. Zeitsch.., vol. Ixviii., 1915 ; 'ibid., vol. Ixxiv., 1916. 



3 Slemons, "Analysis of the Blood in Eclampsia and Allied Conditions," 

 A me): Jour. Obstet., vol. Ixxvii., 1918. See also Emge, "Acidosis in Normal 

 Uterine Pregnancies," Amer. Jour. Obstet., vol. Ixxiv., 1916 ; vol. Ixxvii., 1918. 



