206 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



globulin in a serum solution by means of ammonium sulphate 

 begins at 24-29 per cent, of complete saturation, and is com- 

 pletely thrown out of solution when the saturation reaches 

 46 per cent. The corresponding limits for serum albumin are 

 64 and 90 per cent, of saturation. 



In addition to the salts above mentioned, albumin 

 can be precipitated, as we have seen, by colloidal metallic 

 hydroxides. 



Albumins also combine with numerous organic colouring 

 matters, and advantage is taken of this in the various methods 

 for staining tissues for microscopical examination. Many of 

 the naturally occurring colouring matters exist in combination 

 with albumin, from which they have to be separated if the pure 

 colouring matter is required. In the indigo plant, for example, 

 a portion of the indigo probably occurs in combination with 

 indigo-gluten ; and there is evidence that laccainic acid, the 

 colouring matter of lac dye, exists in the body of the lac 

 insect as an insoluble albumin compound. These facts 

 have their practical importance in connection with dyeing. 

 The reason that wool can be dyed with certain colouring 

 matters which are not taken up by cotton, that is by 

 cellulose, is that wool is chemically related to albumin, 

 and is therefore capable of combining with colouring 

 matters, more especially those of an acid character. Further, 

 various albumins, especially, e.g., serum albumin, as being 

 obtainable in large quantity from the blood of slaughtered 

 animals, is used as a mordant for fixing certain colours in 

 calico printing. 



For the precipitation of peptones and to these may be 

 added enzymes, which we have seen have many of the properties 

 of peptones and are allied to them in composition substances 

 such as phosphotungstic and phosphomolybdic acids may 

 be used. Metaphosphoric acid, and also a mixture of potas- 

 sium ferrocyanide and concentrated acetic acid, can also be 

 used for precipitation of bodies of this class ; it may be 



