184 



MANUFACTURING CELLS 



(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 (44) it will be seen that the maximal rate of 

 secretion occurs some time before the maximal consumption of 

 oxygen, and 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 

 consumption 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 



Fig. 44. — Oxvgen used by the salivary gland during rest, aotivity and restitution. From 

 a to b. the gland was not' secreting, but was using a fairly constant amount of oxygen. 

 From b to c, tlic gland was active — secreting saliva at the rate denoted by the dotted line. 

 From c to d, the gland was being restored to its pre-seeretory state, o-o = oxygen base line. 

 The area, ooss, represents the basal or resting metabolism of the gland. Dark continuous 

 line = oxygen consumption, s-s = base line for saliva. Dotted line = saliva formed in 

 c.c. per minute. (After Barcroft.) 



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 

 of glucose used is parallel to the oxygen consumption, as one would 

 expect. 



The mechanism of secretion has been provocative of much 

 controversy. A regular pitched battle results when vitalists, 

 neovitalists and mechanists discuss the problem. What are the 

 facts ? 



