Feeding and Digestion [ 7 j 



digest starch and glycogen (pH optimum of extract of the amoebocytes is 7.0), 

 and several sugars. '*=- All lamellibranchs and most herbivorous but no 

 carnivorous gastropods have a crystalline style which is an albuminoid mass 

 saturated with amylase, sometimes also containing a weak maltase. '*"'• This 

 style is secreted by the st\le sac (Fig. 29, A); it may be dissolved or re-formed 

 in less than an hour, '-" and is lost from clams kept in air. The style is pushed 

 forward by cilia in the style sac, and the tip wears against a gastric shield which 

 protects the gastric mucosa '-" or aids liberation of amylase. '''■*' '^" The pH 

 optimum of style amylase is: for Ostrea 5.9-6.2, '^" Pecten 6.2, ''- Mactra 

 and Mya 6.5-7.0. ''^- The pH curve for amylase of the style of Mytilufi shows 

 a broad optimal range with peaks at 5.9 and 6.9 on starch and at 6.24 on 

 glycogen. -'^ The amylase of the style of Ostrea acts best at 6.0, whereas that 

 of the digestive diverticula is optimal at pH 6.4. '^-' In carnivorous gastropods 

 the style is absent and a weak amylase is present in the hepatopancreas. 



Amylase is present in gastric fluid and extracts of the hepatopancreas of 

 Crustacea.-'*' '"*• '••" It is reported from the saliva of PeripatopsisJ'-' Amylase 

 is found in secretions of the mid-gut, chiefly from the caeca, of many insects, 

 and in salivary secretions of some such as the cockroach Blatta. "''° The 

 tsetse-fly Glossina has as its only carbohydrase a weak amylase in the mid-gut, 

 whereas a non-blood-sucking fly Calliphora has active amylase in both salivary 

 and mid-gut glands. '^*^ Amylase has been found in the mid-gut of honeybees 

 by some but not by all of those who have looked for it. Starch solution is not 

 drunk in quantity by bees unless combined with sweet syrup; boiled soluble 

 starch can be hydrolyzed in the digestive tract, '"' and bees certainly utilize 

 the starch in pollen. The amylase of most insects acts in a slightly acid medium, 

 but an amylase in the silkworm has an optimal pH of 9.6 or higher. '"^^ 



The caecum of Amphioxus secretes an amylase with pH optimum of 7.0. ^^ 

 All vertebrates have an active amylase in the pancreatic secretion. Hepatic 

 amylase occurs in the bile of chickens, sheep, and cattle. ''- Among mammals, 

 a salivary amylase is found in man, apes, elephant, and pig. Its occurrence is 

 doubtful or slight in rodents, dogs, and several ungulates. ^"'^ Salivary amylase 

 is generally present in birds and a trace occurs in frogs. '^' Human salivary 

 amylase has a pH optimum of 6.2, contrasted with an optimum of 6.8-7.1 for 

 pancreatic amylase. 



It is probable that all animal amylases are similar, despite slight differences 

 in pH optima. All appear to be a-amylases. The animal amylases are activated 

 by CI ions (in NaCl) and lose their activity on dialysis. '""' flydrolytic 

 digestion of glycogen is brought about by amylase and there is probably no 

 specific glycogenase. 



Cellulose Digestion. Enzymes which attack cellulose have evolved inde- 

 pendently in several diverse groups of organisms. Digestion of cellulose by 

 putrefactive bacteria and fungi is well known, but cellulase has not been 

 studied in any free-Hving Protozoa, except Vampyrella. However, several 

 groups of parasitic Protozoa can digest cellulose. 



Cellulases have been found in digestive extracts of earthworms, some snails 

 {Helix and Limnaea), and the wood-boring bivalve Teredo. Extensive studies 

 of the kinetics of Helix cellulase were made by Karrer, '^^ and the difference 

 from plant cellulase was pointed out. ''*' Wood contains various carbohy- 

 drates, cellulose, hemicellulose, lignin, starch, and sugars, and wood-dwelling 



