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THE BIOLOGY OF HYDRA : 1961 



comes from the later injection of culture solution that has been 

 enriched with dissolved COo gas. 



The final step in the twice daily setting of pH, pOs, pNHg and 

 pCO^ involves setting the oxygen tension. Since oxygen is only 



*>v s^^« 



Fig. 5. The pCOo of a culture is adjusted by injecting a calculated 

 amount of culture solution that has previously been bubbled for ten 

 minutes with gas from a tank of compressed air containing 10% CO.. (see 

 tank behind technician). This COj-rich water is stored in the large 100 ml. 

 syringes on the bench for later use. Such syringes are filled with a long 

 glass tube from the bottom of the tall cylinder as illustrated. 



slightly soluble in water, pOo is set by adjusting the air phase 

 and then allowing the shaking machine to keep the air and water 

 phase in equilibrium. In practice, a 100 ml. syringe is filled with No 

 from a tank and then partially emptied and refilled to 100 ml. witli 

 room air, the syringe thus containing whatever dilution of air in 

 nitrogen that one desires. A needle is attached to the syringe and the 



