PHYSIOLOGY OF THE INVERTEBRATA. 177 



lectiou of the blood in vacuo (from the time of leaving the 

 vein, &c.) without any alteration in its composition. The 

 glass receiver AOD (left-hand figure), in which the vacuum 

 is made, has a canula E fastened to its lower end. The 

 canula is drawn out into a fine capillary point, which is 

 pushed into the artery, vein, or under the hypodermis, as the 

 case\ may be. After introducing the canula into the blood 

 system, the tap B is opened, and the blood rises into the 

 receiver. The gases are evolved almost immediately, and by 

 means of the pump they are collected over mercury in the 

 tube ah, where their composition is ascertained. 



After the introduction of the blood into the receiver the 

 tap B is turned ofi"; the receiver is then attached to the 

 pump. Before opening the tap A, the receiver is placed in a 

 bath of water heated to about 40° C. The heat assists in the 

 liberation of the gases from the blood. Coagulation is pre- 

 vented by previously introducing a small quantity of sodium 

 chloride into the receiver (i.e., before the introduction of the 

 blood).* 



The pump and pneumatic trough do not require description, 

 as they are of the usual kind. The volume of the mixed 

 gases collected at ah having been ascertained, the percentage 

 of each gas is estimated by the ordinary methods of gas 

 analysis. The carbonic anhydride is absorbed by potash, 

 the oxygen by pyrogallic acid, whilst the amount of nitrogen 

 is represented by what remains. 



(a) Blood of Sepia officinalis. 



A hundred volumes of the blood of the cuttlefish contained 

 the following volumes of the three gases — the volumes being 

 reduced to 0° 0. and 760 mm. : — 



* The liberation of carbonic anhydride is accelerated by previously 

 introducing into the receiver a small quantity of a hot solution of tartaric 

 acid. 



M 



