150 



MANUFACTURING CELLS 



(b) Restitution. Just as in muscular, so in glandular activity 

 the great proportion of the oxygen used is associated with the 

 phase of restitution. Energy is required for the building up of 

 material to replace that lost during secretion. 



(c) Then, as in muscle, the gland requires a certain amount 

 of energy for domestic use. To keep its parts in repair and to 

 preserve its identity, it requires a maintenance allowance. The 

 following figure from Barcroft will help the student to realise the 

 energy expended during these three phases in the activity of the 

 salivary gland in the cat. 



From the figure it will be seen that the maximal rate of secretion 

 occurs sometime before the maximal consumption of oxygen, and 



MINS. 



a "b c d 



FIG. 2C. Oxygen used by the salivary gland during rest, activity and restitution. 

 From a to b, the gland was not secreting, but was using a fairly constant amount of 

 oxygen. From b to c, the gland was active secreting saliva at the rate denoted by tin- 

 dotted line. From c to '/, the gland was being restored to its pre-secretory state. 

 0-0 = oxygen base line. The area, ooss, represents the basal or resting metabolism 

 of the gland. l)ark continuous line = oxygen consumption. s-s=base line for 

 saliva. Dotted line = saliva formed in c.c. per minute. (After Barcroft.) 



that the increased consumption of oxygen lasts for some time 

 after the saliva has ceased to flow. Barcroft and his colleagues 

 found that the length of this period of increased oxygen con- 

 sumption depended upon the previous degree of activity of the 

 gland as well as on its functional capacity. In other words, if a 

 previous inroad upon the store of material had not been made 

 up, the factory cells would have to work at high pressure to keep 

 pace with the demand. Work at high pressure is not economical. 

 Each gram of secreted material is formed at an increased cost in 

 oxygen and energy. 



The energy required for secretion comes from the oxidation of 

 glucose. (Again compare with muscle.) For the dispatch of 

 the material, little extra oxygen and little extra glucose is required. 

 Asher and Karalov found that the restitution phase required the 

 most energy. That is, the glucose content of the blood was 

 markedly diminished in the post-secretory period. The amount 



