en. xxxi.] METT'S TUBES 489 



have furnished us with the key to the problem ; just as poisons introduced from 

 without stimulate the cells to produce antitoxins, so harmful substances produced 

 within the body are provided with anti-substances capable of neutralising their 

 effects ; for this* reason the blood does not normally clot within the blood-vessels, 

 and Weinland has shown that the gastric epithelium forms an antipepsin, the 

 intestinal epithelium an antitrypsin, and so on. 



Mett's Tubes. 



A method which is now generally employed for estimating the proteolytic 

 activity of a digestive juice is one originally introduced by Mett Pieces of 

 capillary glass tubing of known length are filled with white of egg. This is set into 

 a solid by heating to 95 C. They are then placed in the digestive fluid at 36 C., 

 and the coagulated egg-white is digested. After a given time the tubes are 

 removed ; and if the digestive process has not gone too far, only a part of the little 

 column of coagulated proteid will have disappeared ; the length of the remaining 

 column is easily measured, and the length that has been digested is a measure of 

 the digestive strength of the fluid. 



Hamburger has used the same method in investigating the digestive action of 

 juices on gelatin. The tubes are filled with warm gelatin solution, and this jellies 

 on cooling. They are placed as before in the digestive mixture, and the length of 

 the column that disappears can be easily measured. These experiments must, how- 

 ever, be performed at room temperature, for the usual temperature (36 40 C.) at 

 which artificial digestion is usually carried out would melt the gelatin. He has also 

 used the same method for estimating amylolytic activity, by filling the tubes with 

 thick starch paste. 



Schiitz' Law. 



E. Schiitz stated in 1885 that the amount of peptic activity is proportional to the 

 square root of the amount of pepsin. This was confirmed by Borissow, who used 

 Mett's capillary tube method. An example (taken from the work of E. Schiitz, who 

 estimated the amount of the digestive products in solution by means of nitrogen 

 determinations) will suffice. 



Amount of Solution Digested Nitrogen in Grammes. 



of Pepsin in 

 Cubic Centimetres. Found. Calculated. 



1 0-0230 0-0223 



4 0-0427 0-0446 



9 0-0686 0-0669 



16 0-0889 0-0892 



This work was an early attempt to deal with enzyme action on exact mathemati- 

 cal lines, a branch of the subject now being extensively studied. Some have stated 

 that the law holds more or less exactly for other enzymes ; in other cases the rela- 

 tionship is different. The usual method now adopted is to estimate the velocity of 

 reaction, that is, the time occupied by the ferment in accomplishing a given end on 

 a fixed amount of material. If, for instance, one takes a series of tubes, each con- 

 taining the same amount of milk, and adds to each different known amounts of 

 rennet, the time occupied in producing curdling is accurately noted. In this case, 

 and in similar experiments with blood or blood-plasma and fibrin ferment, the 

 amount of ferment multiplied by the coagulation time is constant ; thus, if two drops 

 of rennet produce coagulation in 30 seconds, four drops will curdle the same amount 

 of milk in 15 seconds. The same simple relationship also probably holds for the 

 action of invertin, erepsin, and trypsin. 



