THE PRECIPITINS AND THEIR ANTIBODIES 285 



instance, from lacto-serum by means of milk), it yields no 

 antiprecipitin on being heated ; normal serum likewise 

 gives no antiprecipitin. 



The binding of precipitin to casein may be judged, on 

 the basis of the insignificant solubility of the compound, to 

 be nearly complete if the two substances are present 

 in equivalent quantities. If one of them is present in the 

 fluid in excess, it is to a large extent carried down by the 

 precipitate. Especially is this valid for precipitin. With 

 the precipitable substance there is another perturbing 

 influence, which is especially prominent with egg-albumen 

 and which has its analogies in the behaviours of agglu- 

 tinins and serum-precipitins. An excess of egg-albumen 

 dissolves the precipitate, so that it is often observed that 

 a given quantity of precipitin causes a precipitate with a 

 weak but not with a stronger solution of egg-albumen. 

 Even with casein this peculiarity may be observed, as 

 Miiller's later experiments indicate. The quantity of the 

 precipitate produced by a given quantity of lacto-serum 

 therefore increases at first with the quantity of casein 

 added, and reaches a maximum in the neighbourhood of the 

 point where the casein added is equivalent to the quantity 

 of lacto-serum, only to decrease thereafter and fall to zero 

 at a point where the quantity of casein added is nearly 

 double that corresponding to the maximum value; the 

 determinations do not seem to be accurate enough to 

 warrant more than an approximative valuation. 



Some experiments of Eisenberg afford an idea of the 

 relations between antiprecipitin and precipitin. The quan- 

 tities of the preparations are given in drops. The antiserum 

 was heated precipitin diluted in the proportion I to 5. 



