FOODS AND CONDIMENTS 173 



in a position to replace with simpler methods some protracted metab- 

 olism experiments. I might incidentally mention the methods of 

 adsorption and staining which hitherto have not been sufficiently 

 considered. In the various food preparations (whose names need not 

 be mentioned), it is quite unessential whether they contain a few per 

 cent more or less of carbohydrate or nitrogen, a fact which is always 

 especially emphasized in the advertisements; whereas it is quite 

 important to know their swelling capacity, and whether this permits 

 their complete and rapid utilization in the alimentary canal. 



Milk and Dairy Products. Milk, as a physiological excretion will 

 be considered on pages 345, et seq., and there also much is said which 

 pertains to its properties as a food material. Here we shall concern 

 ourselves merely with the examination of milk. The present-day 

 methods of milk examination are limited to certain characteristics 

 which are especially easy to determine and, therefore, are easily 

 simulated by adulterators. Pure food officials lay most stress on 

 the water and the fat content. Sometimes, in addition, they de- 

 termine the protein percentage, preservatives, and the possible ex- 

 istence of disease organisms. Inasmuch as milk is by far the most 

 valuable food-stuff, it is of the greatest importance not only to 

 determine variations produced under the normal circumstances by 

 adulteration, but also those occurring under normal conditions of 

 production, change of fodder dependent upon change of season, 

 natural and artificial fodder, boiling, pasteurization, etc. Accord- 

 ingly, H. ZANGGER* 2 and his pupils undertook to discover new 

 methods; in them he regarded milk as a solution of colloids and 

 electrolytes Of the colloid methods, ZANGGER and his pupil, 

 KOBLER, have chosen the determination of surface tension, which 

 proved to be one of the "most complicated but perhaps the most 

 delicate and flexible method." Among the various procedures, the 

 bubble method, in which bubbles are allowed to form in the fluid, 

 gave the most constant results. 



Normal milk gave quite constant figures. Inasmuch as by this 

 method only such substances have an influence as are forced to 

 the surface, these can make themselves evident in the minutest 

 quantities. Adulteration with water is not easily detected by this 

 method. Fermentation, on the contrary, causes great departures 

 from the normal, which are explained by the development of fatty 

 acids. The addition of alkalis also changes the surface tension. 



By the study of the viscosity, abnormal protein and fat content 

 could be shown and likewise additions (adulterations) which in- 

 fluenced the amount of swelling (especially alkaline additions) . The 

 viscosity is also diminished by violent shaking, though milk regains 



