FERMENTS. 477 



have a toxic effect when injected subcutaneously. Hildebrandt 1 found 

 that the lethal dose for a medium-sized rabbit was . 1 gram for pepsin, 

 invertase, and diastase; 0.05 gram for emulsin and myrosin; and 2 grams 

 for rennin. All of the injected ferments caused rise of temperature. 

 Dogs, which had had ferments injected, would not eat, showed thirst, trem- 

 bling, restlessness, an unsteady gait, and eventually coma. Rabbits 

 showed principally emaciation, weakness, and sometimes extensor con- 

 vulsions. Such observations necessarily have only a relative value, 

 owing to the fact that the nature of the ferments is still unknown, so that 

 their purity cannot be estimated. 



On the other hand, the formation of the anti-ferments and the observed 

 normal occurrence of these, gives us an indication of the role which, for 

 example, the ferments absorbed by the intestines perform in their circu- 

 lation through the body. We can easily imagine that the organism par- 

 alyzes the activity of the absorbed ferments by the production of the anti- 

 ferments. The presence of such substances also suggests an explanation 

 of how the living tissue is protected against self-digestion. 2 We can also 

 imagine that this protection is obtained by the cells altering the material 

 which they require for constructive purposes, and do not wish to consume, 

 so that the ferments are unable to find any point of attack. It is certainly 

 not without significance that the connective tissue, e.g., elastin and 

 substances like spongin and silk-fibroin, which are not considered as 

 nutrient materials, contain in large quantities just those amino acids 

 which make hydrolysis difficult. The substances are, as a matter , of 

 fact, hardly attacked by pepsin-hydrochloric acid or by trypsin. The 

 cell has only to cause a slight rearrangement of the atoms in the mole- 

 cules of the assimilated products to form modifications which the fer- 

 ments are not able to attack, or it may cause them to combine with other 

 cell-components. 



An unsolved problem is the origin of the ferments. It has often been 

 suggested that they bear a definite relation to the food. In fact, many 

 observations indicate a close connection between the production of fer- 

 ments and the assimilation of the food. We merely do not understand 

 the more intimate relations existing between the two processes. Brown 

 and Morris 3 have shown that the leaves of many plants contain the most 

 diastase in the morning, the amount decreasing during the day. If the 

 assimilation is carried out in the sunlight, the formation of diastase ceases 



' Virchow's Arch. 121, 1 (1890); 131, 26 (1893). 



2 E. Weinland, Z. Biol. 43, 86 (1902), has found such anti-ferments in cell-free 

 extracts of parasitical worms. Extracts from the mucous membranes of the stomach 

 and intestine, as well as erythrozytes, are credited with retarding the solution of fibrin. 

 Z. Biol. 41, 1, 146 (1902). 



3 J. Chem. Soc. 62, 604 (1893); 57, 493 (1890). 



