CHAPTER IX 

 THE PRECIPITINS AND THEIR ANTIBODIES 



IN many instances the reaction-products of the ferments 

 are solid bodies, and such ferments are called precipitins. 

 Generally these solid substances contain a great deal of 

 water, like albuminous substances in general ; and this cir- 

 cumstance has in recent times led to the opinion that the 

 act of precipitation might consist only of a coalescence and 

 subsidence of the "colloidal" particles of the particular 

 albuminous substance in the system. Thus, for instance, 

 the casein of milk is, according to this theory, present in 

 the state of so-called pseudo-solution. Its smallest parti- 

 cles may be regarded as an extremely fine solid powder of 

 ultramicroscopic magnitude (dimensions less than .0002 

 millimeter). On the addition of rennet these solid particles 

 coalesce to form larger clumps and subside, just as finely 

 powdered clay sedimentates following the addition of salts 

 or acids to the water in which it is suspended. 



In corroboration of this view Duclaux l cites the follow- 

 ing observation. "In milk, which is turning sour but 

 which is still quite liquid, we observe with the miscroscope, 

 as I have indicated, a precipitate of fine grains, which at the 

 beginning are seen only with difficulty, and are detected 

 only by a faint disturbance of the visional field, but 

 which later on display quite distinct granulations, charac- 

 terised by the Brownian movement, just as minute particles 



1 Duclaux: Microbiologie f 1omQ 2, pp. 253-339 (1899). 

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