1176 



PHYSIOLOGY 



rises into Y it carries before it a glass valve which prevents its further passage, 

 so that it can only escape by the tube c, driving before it all the air previously 

 contained in B. The water-supply is now turned off, and the tap to the sink 

 turned on. The mercury runs back. Air cannot enter by c, since this tube is 

 sealed by mercury. The valve Y therefore sinks and allows the air in the blood 

 receivers G, G and the rest of the apparatus to escape into B. This process is repeated 

 many times until a high vacuum is produced in the whole apparatus. A measured 



FIG. 491. Barcroft's modification of the Topler pump. 



quantity of blood is now let into the lower bulb G. r is a condenser through which 

 cold water is constantly flowing (to prevent all the blood boiling away), while 

 warm water circulates round the bulbs G, G to facilitate the giving off of the blood 

 gases. The blood boils in the vacuum, and the gases escape into B, and may be 

 driven off and collected over mercury in a cylinder D by raising the mercury in B. 

 The process of exhaustion is repeated until no more bubbles rise into D on filling 

 the bulb B with mercury. E is a sulphuric acid chamber for drying the gases as 

 they pass from the blood to the bulb B. 



In this way, from 100 c.c. of blood, about 60 c.c. of mixed gases 

 may be obtained, consisting of oxygen, carbon dioxide, nitrogen, and 



