The Biology of Senescence 



According to Hodge, the cell-number in the brain of old 

 workers was reduced by three quarters. Pixell- Goodrich found 

 that in diseased, and therefore inactive, workers, the cerebral 

 architecture was more normal than in healthy workers. Schmidt 

 attributed the reduction in cell size and cell-number to direct 

 'wear by use', the amount of work done by the insect being a 

 fixed quantity. Holmgren (1909) found a similar deterioration 

 in the supraoesophageal ganglia of old termite primaries: the 

 brain of old physogastric queens of Eutermes was reduced to 

 two thirds of the volume usually found in virgin queens. 

 Another instance of 'Gehirntod' in insects was described by 

 Hansemann (1914) in Bacillus rossi (Phasmidae). 



Quite apart from the fact that they have been indiscrimin- 

 ately transferred to mammals, these findings themselves have 

 been open to intermittent criticism. 1 Smallwood and Phillips 

 (1916) were by no means satisfied that the changes in relative 

 nuclear size described by Hodge in worker bees resulted from 

 ageing or were in any way pathological. Weyer (1930) regarded 

 the cerebral ganglion changes as secondary, since the supposedly 

 senile degeneration appears remarkably suddenly, and only 

 after evident deterioration in other organs. In a 5-year-old 

 queen, Pflugfelder (1948) found some disturbances of cerebral 

 histology especially in the corpora pedunculata, but no sig- 

 nificant cerebral change in old drones and workers. Rockstein 

 (1950), however, found a decline in cell-number in the brain of 

 worker bees from a mean 522 at eclosion to 369 at 6 weeks. The 

 complex behaviour of worker bees deteriorates suddenly just 

 before death, moreover. 



Schulze-Robbecke (1951) made a careful search for evidence 

 of 'cerebral death' in Dixippus and Melolontha and found no signs 

 of it whatsoever, the primary senile deterioration being most 

 evident in gut and musculature. 'Vielleicht hat v. Hansemann 

 bereits tote Tiere untersucht, was sehr leicht vorkommen kann, 

 da bei den Stabheuschrecken infolge ihrer Reaktionstragheit 

 der Ubergang von den letzten Lebensausserungen zum Tode 

 nicht ohne weiteres festzustellen ist.' The amount of senile 

 change described either as a result of fixation-artefacts or the 



1 The large literature of neurone loss with increasing age in mammals, 

 especially in the cerebellum, is reviewed by Andrew (1955). 



100 



