The Precqntum 99 



also by weak formalin, both of which are known to coagulate albumin, 

 the solutions thus treated being no longer precipitable. Nevertheless 

 the albumin retained its affinity for precipitin. Eisenberg and Volk 

 have made analogous observations upon agglutinins. Michaelis and 

 Oppenheimcr (1902, p. 347) refer to the earlier observations on toxins 

 as possibly throwing some light upon the nature of the precipitable 

 substance. The toxins were at first considered albuminous, and for this 

 reason called toxalbumins. Further investigation showed that they 

 might be freed from albumin. Thus Brieger (1895) and others prepared 

 tetanus toxin which gave no biuret reaction, Jacoby (1900-1) did the 

 same with ricin, and Hausmann (1902) with abrin. Nevertheless 

 Michaelis and Oppenheimer consider that both in the case of toxin and 

 precipitable substance these substances may be simply torn away from 

 the large albuminous molecule to which they naturally belong. 



The Precipitum. 



According to Tchistovitch (v. 1899) the precipitum is soluble in 

 dilute acids and alkalis; insoluble in water, solutions of neutral salts and 

 alkaline carbonates. Nolf (v. 1900) considers the precipitum a globulin, 

 giving as evidence thereof that a precipitin added to globulin and 

 albumin solutions separately or mixed, yields a precipitum. Tchisto- 

 vitch states a precipitum is only formed in alkaline solutions, although 

 there may be some opalescence in neutral solutions, whereas acid 

 solutions remain clear. The precipitum (from eel and anti-eel serum) 

 proved non-toxic to rabbits when administered intravenously, although 

 the clear supernatant fluid proved toxic when it contained unneutral- 

 ized ichthiotoxin\ 



Bordet (iii. 1899) found different precipita soluble in dilute alkali. 

 Leclainche and Vallee (25, i. 1901) state that washed precipitum 

 gives all the albumin reactions. Leblanc (31, v. 1901, p. 362) states 

 that a repeatedly washed precipitum, obtained by adding anti-ox 

 globulin (from rabbit) to ox globulin solution, had a jmik tint, due to 

 haemoglobin which had doubtless entered into union with the precipitin. 

 Nitrogen estimations made before and after precipitation lead to the 

 same conclusion regarding the occurrence of a union. Moro (31, X. 1901) 

 found that a lacto-precipitum was almost entirely dissolved in warmed 

 salt solution. Eisenberg (v. 1902, pp. 307-8) has also found lacto- 

 precipitum to be soluble at higher temperatures, being different in 



^ Ichthiotoxin, see p. 39. 



7—2 



