THE PRECIPITINS AND THEIR ANTIBODIES 269 



casein does not pass through is explained by Duclaux as 

 due to its state of pseudo-solution, which is really only a 

 mode of expression and no real explanation ; and the same 

 property may be characteristic of the serum-albumen, 

 especially if the filter is covered by a gel of casein. 



The addition of a solution of an oxalate or of a fluoride 

 to milk inhibits its coagulation. One might suppose this 

 action to be due to the precipitation of the calcium from 

 the compounds of the milk and of the rennet. Duclaux 

 combats this view and states that the coagulation is not 

 inhibited if the oxalate (or fluoride) is not present in excess. 

 He assumes that the oxalate or fluoride has itself a direct 

 influence upon the milk, lowering its tendency to coagula- 

 tion. From the modern point of view of physical chemistry, 

 it seems quite obvious that for the coagulation a certain 

 degree of concentration of the calcium ion (or barium or 

 strontium ion) is necessary. The more oxalate present, the 

 lower would be this concentration, so that a certain concen- 

 tration of the free oxalate ion (or fluorine ion) is necessary 

 to prevent coagulation. This concentration probably de- 

 pends in part upon the temperature. 



Another coagulation process of especial interest is the 

 precipitation of blood-plasma by means of fibrin-ferment 

 (cf. p. 91). This process is very similar to the coagula- 

 tion of milk or casein, but seems to be different in the fact 

 that coagulation of the plasma can occur spontaneously. 

 According to Duclaux, this depends upon the action of 

 the leucocytes present in the blood. In their cytolysis 

 they form a coagulating ferment. Coagulating ferments 

 that act upon blood-plasma are very common in the differ- 

 ent tissues, fluids, and organs of the body. Alexander 



