2 Mr Bar croft, Apparatus for Analysis of the Gases, etc. 



or to put the matter in another way, my object has been to secure 

 the same error in the figures when worked out as percentages 

 as others have done, while using only a fifth of the blood for 

 analysis. 



The most obvious source of error is, of course, the contamina- 

 tion of the blood gases with small quantities of air, and it will 

 be apparent that, in an apparatus the parts of which are de- 

 tachable, it is almost impossible to avoid small leakages. 



In the present apparatus there are no joints to be made, as 

 the whole is in one piece. This arrangement would be simple 

 were it only necessary to collect one sample of blood ; the present 

 apparatus however provides for the collection of nine samples, 

 six from a vein, and three for comparison from an artery. 



With regard to the errors of the apparatus, the greatest is that 

 of measuring the blood, as the surface of the mercury beneath 

 it is sometimes broken by films of blood ; the extreme error 

 here is '05 c.c. Another error is produced by the fact that a film 

 of blood is left over the glass in a tube leading to the chambers 

 and in the burette. This is a very variable quantity and depends 

 in the first place upon the individual apparatus, and in the second 

 place upon the tendency of the blood to coagulate. If the blood 

 is very fluid, and the apparatus carefully made with the tube 

 straight and of 2 millimetres diameter, the amount of blood then 

 left as a film is about '05 c.c. Each sample will therefore be con- 

 taminated to that extent by the previous one. 



In regard to the collective error of the whole apparatus, the 

 following analysis of defibrinated blood will serve as a guide. 



Analysis of three samples of the same defibrinated blood : 



CO, 23-7 23-9 24*0 c.c. 

 O 20-4 20-2 20-6 c.c. 

 N 1-9 1-7 1-9 c.c. 



On another occasion three samples gave respectively, 



CO, 52-6 526 527 c.c. 

 O 119 119 119 c.c. 

 N 1-6 2-4 19 c.c. 



Description of Apparatus. The Pump. 



The Toepler Pump has been employed, without any modifica- 

 tion except that the drying apparatus is so arranged that the 

 sulphuric acid can be renewed without introducing more air into 

 the apparatus than what is dissolved in the acid. 



A three-way tap, Fig. 1 (c), leads to a water-pump which 

 gives a vacuum, almost up to the tension of aqueous vapour. 



