size. This probably means that the fhes without m. ii. c, just like the sugar- 

 fhes, must be able to utihze the species specific protein of the pupal fat-body 

 for the shght initial growth of the organs, whereas they only seem to be able 

 to utihze a very small amount of the meat they do in fact eat. On the basis of the- 

 se findings the working hypothesis was tentatively advanced that the medial 

 neurosecretory cells in some way influence protein metabolism. However, 

 nothing could be said as to Ьолу this postulated effect was brought about. 

 It might be that the operated flies ate less than normal flies, or that the 

 ingested food was not properly digested, or that the resynthesis of the absorbed 

 aminoacids was inhibited. The amazingly constant size of the egg-chambers 

 of fhes + m. n. с is in favour of the suggestion that the synthesis is blocked. 

 In previous studies it has also been found that the two nervi oesophagei which 

 pass from the corpus cardiacum -f ganglion hypocerebrale to the intestine 

 contain neurosecretory material, which is probably produced by the medial 

 neurosecretory cells. The cutting of these nerves caused a retardation of the 

 growth of the ovaries. These observations suggest that the m. n. с might 

 have an influence on digestion. Also Wigglesworth's observation in Rhodnius 

 (1948) that decapitation delays digestion of the blood meal points in this 

 direction. Therefore a series of experiments was undertaken to study the 

 proteinase activity of the gut of normal flies and that of fhes deprived of their 

 m. n. с 



The proteinase activity of the gut was determined by means of the colori- 

 metric method used by Day and P owning (1949) originally described by 

 Charney and Tomarelli (1947), only we kept the homogenates for 4 hours 

 in the incubator instaed of one. Using homogenates both the amount of protei- 

 nase in the lumen of the gut and that of the gut cells is measured. 



We measured the proteinase activity of the midgut of 5 categories of flies: ^) 

 7—9 hours old, unfed females, 2) normal 5 days old females, =^) 5 days old 

 sugarflies,^) о days old females which had their m. n. с removed when 5 — 9 

 hours old, and') 5 days old operated controls. Apart from the sugarfhes, the 

 flies were fed on meat, sugar and water. All the flies were kept at 25°C. 



The result of a first series of experiments has been published in a preliminary 

 paper in "Nature". (E. Thomsen and I. Möller, 1959). 



In a second series of experiments the midguts Avere removed 8—10 hours 

 after the beginning of the last meal. As we got higher values for the readings 

 when using 440 т[л instead of 480 т[л used in the first series, this wavelength 

 was used for the readings in this series. The flies луеге not starved before they 

 got the last meal. 



We should have preferred to calculate the values per weight of midgut, 

 but this was found impossible, because if we starved the flies in order 

 to obtain empty guts, the proteinase activity of the normal fhes dropped 



123 



