258 PHYSIOLOGY CHAP. 



acid must primarily be referred to the constitution of its epithelial 

 cells. Yet it seems to us essential to recognise that the sub- 

 epithelial tissues also present a considerable resistance, otherwise 

 we cannot explain why extensive interruptions in the continuity 

 of the mucous coat can be repaired before the tissue is digested. 



Even before Matthes, and independent of him, this problem 

 was treated in a yet more general form by Fermi (1890-95), who 

 brought new evidence to support the thesis that living protoplasm 

 cannot be attacked by the proteolytic enzymes. He called attention 

 to the bacteria and animal and vegetable parasites that swarm in 

 the alimentary canal, referring to facts that were already partly 

 known, but that no one had thought of invoking in connection 

 with this subject. 



Fermi observes that Hyphornycetes and Blastornycetes live and 

 multiply in both natural and artificial gastric juice, and modify 

 its reaction and digestive activity ; that trypsin in alkaline 

 solution is inactive in vitro to the whole class of Schizomycetes, 

 which, indeed, live and multiply upon it ; that Amoebae consisting 

 of naked protoplasm are neither digested by trypsin in vitro nor 

 in the intestine ; that the seeds of Graminaceae and Leguniinosae 

 nourish and germinate well in sterilised solutions of active trypsiu ; 

 that, lastly, worms and insect larvae immersed in solutions of 

 trypsin are in no way attacked, and that Lumbricidae and 

 Ascaridae find the proper medium for their development and 

 reproduction in the intestines of animals. 



Fermi further notes that sterilised active trypsiu can be 

 injected in strong and repeated doses (2 grins, per diem for a week) 

 under the skin of living guinea-pigs, without producing any 

 symptom of digestion. It is not absorbed, but is destroyed in situ 

 by the living protoplasm of the tissues. Ten minutes after 

 injection in the guinea-pig, and five hours after in the frog, it is 

 no longer possible to find a trace of trypsin anywhere in the body, 

 even with the highly sensitive gelatin method gelatin, according 

 to Fermi, being liquefied even by the most dilute solutions of 

 trypsin. When mixed with freshly minced organs of newly killed 

 animals, the trypsin disappears completely after 24 hours. This 

 is not the case when the organs have been previously boiled. 



The so-called digestion of living tissues is due to the deleterious 

 action of hydrochloric acid, which alters or kills the cells prior to 

 their digestion by pepsin. This action is promoted by temperature. 

 In effect the tissues of a living frog resist the solvent action of 

 the gastric juice in vitro at 15-20 C. ; while they are digested at 

 the temperature of 38 C. at which 1'avy, Bernard, and others 

 experimented. The cells of the gastric mucous membrane are 

 specialised cells, adapted for living in the presence of hydrochloric 

 acid, like the cells of the sulphuric acid glands of certain 

 Gasteropoda which tolerate this acid in 4 per cent solutions, like 



