22 THE PHYSIOLOGY OF EARTHWORMS 



an end product of digestion when intestinal extracts are mixed with 

 chitosan hydrochloride at pH 5, indicating chitinase activity. 

 Insufficient material was available to demonstrate the presence of 

 this enzyme in all species but both chitinase and cellulase are 

 found in A. longa, A. caliginosa^ A. chlorotica, Lumbrkus rubellus 

 and Octolasium cyaneum, cellulase only being found in Dendrohaena 

 mammalis and Bimastus eisenii. 



The secretion of these enzymes is also a localized affair since very 

 little sign of activity is found in extracts of pharynx, oesophagus, 

 crop or gizzard. The greatest production occurs in the anterior 

 segments of the intestine, only one-tenth of the cellulase and one- 

 third of the chitinase activity of the anterior end being present in 

 the rear portion. It is suggested that these enzymes are actual 

 products of the earthworm gut itself (Tracey, 1951), but in view of 

 the digestion of cellulose by symbiotic bacteria and protozoa in the 

 alimentary canal of other animals such as cows and the shipworm 

 Teredo further evidence is required before its final acceptance. 



This may, in fact, be partially provided by Parle (1960) who has 

 subjected the intestinal wall to considerable washing before 

 preparing extracts and has found that cellulase and chitinase are 

 still present in fair quantities. Under these conditions it is unlikely 

 that the cellulose decomposers in the intestinal flora and fauna 

 increase to a high enough level to cause appreciable breakdown of 

 cellulose in the time available. The evidence points towards a 

 production of cellulase and chitinase by the earthworm itself, but 

 strictly controlled experiments are still required. 



Analysis of worm casts shows that optical rotation of light follows 

 incubation with 20% saccharose at pH 5-5-6-0, due probably to an 

 invertase enzyme originating in the gut. The activity in casts is 

 twice that available naturally in the soil, though it may just as 

 easily be a by-product due to the intestinal flora and fauna which 

 are bound to be associated with cast material (Kiss, 1957). 



Each of the enzymes present, protease, amylase, lipase, cellulase 

 and chitinase each have a distinctive optimum pH, but little 

 variation in pH occurs along the length of the gut. The upper and 

 lower limits in L. terrestris are pH 6-3 and pH 6-6 respectively as 

 judged by indicator dyes. Electrometric methods of estimating 

 pH have been used on other species e.g. Allolobophora savigjiy 

 (Pu)1:orac and Mauret, 1956) and indicate that the anterior part of 



