2 7 were pasteurized. This is, no d o u b t , below t h e t r u e figure on account of t h e fact t h a t t h e samples are t a k e n uniformly from t h e different dealers a n d not in proportion t o t h e size of their routes; t h e dealers selling t h e most milk are without d o u b t those who sell t h e pasteurized milk, while t h e m a n with t h e small route generally sells raw milk. T h e number of adulterated samples are about t h e same as found i n past years. T h e laboratory

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... s would indicate t h a t there is more watering done b y t h e producer a n d more skimming is practiced b y t h e small retailer. T h e adulteration of milk is not as a rule carried on b y t h e same men. We make b u t few complaints in court alleging a second offense, for after one prosecution t h e convicted person either ceases t h e adulteration, or else goes out of t h e business. T h e actual market conditions are better in this respect t h a n our figures show because we collect such a large n u m b e r of samples from suspected persons. KO d o u b t less t h a n 2 per cent of our milk supply is subject t o adulteration. T h e alcohol precipitation test showed t h a t j.2 per cent of t h e total samples a n d 4.1 per cent of t h e pasteurized samples were sufficiently old when t h e y reached t h e laboratory t o curdle on boiling. T h e results of t h e 11. reductase test showed t h a t 5.6 per cent of t h e samples collected during seven months were t o o old t o use as food when t h e y reached t h e laboratory. If these samples could have been tested a t t h e time of taking, t h e figures would have been lower during t h e summer months b u t not much difference could have been expected during cold weather. T h e pasteurized samples were better in this respect t h a n t h e raw samples. These figures are higher t h a n would be consistent with a thoroughly hygienic milk supply for if 94 per cent of t h e samples reached t h e laboratory in good condition t h e other 6 per cent collected a t t h e same time n-ould have done so if fresh. An example of very old milk was shown in t h e samples furnished t o a cont r a c t o r , which were nearly sour when t h e y reached t h e laboratory, about t w o hours after being delivered b y t h e producer. It is fortunate t h a t these conditions are unusual or i t would be impossible for t h e consumers in congested districts t o obtain a n y sweet milk. S U M MIA RY I . It is possible t o detect commercial pasteurized milk b y t h e Schardinger reaction b u t not b y t h e peroxidase reaction. 2. T h e a m o u n t of pasteurized milk on t h e market is greatest in t h e large districts. 3. T h e airerage quality of t h e milk is considerably above t h e legal standard. 4. The average quality of t h e pasteurized milk is very slightly below t h a t of t h e r a w milk b u t this does not appear t o be due t o adulteration. j. Pasteurized milk shows less fluctuation in composition t h a n raw milk, a n d t h e percentage of samples below s t a n d a r d is less of t h e former. 6. Fresh milk will not coagulate with a n equal volume of 68 per cent alcohol. ;. Sinety-four per cent of t h e samples delivered a t t h e laboratory gave reactions for fresh milk; t h e balance was too old for use as fresh milk. I wish t o acknowledge m y indebtedness t o m y assistant hfr. Lewis I. Nurenberg for collaboration in t h e experimental a n d routine work, a n d t o N r . Henry N. Jones for making t h e bacterial counts. T h e usual method fo? t h e detection of gelatin in food products such as milk or cream a n d t h a t adopted provisionally by t h e United States Department of Agriculture' consists in t h e removal of t h e proteids with acid mercuric nitrate a n d t h e precipitation of t h e gelatin in t h e filtrate with picric acid. I t , however, has been frequently noticed t h a t a sweet cream IThich gave no precipitate with picric acid would, after souring, show quite a perceptible turbidity on i t s addition, often heavy enough t o lead t o t h e assumption t h a t gelatin was present. I t seems most probable t h a t this is due t o protein decomposition products not precipitated by t h e acid mercuric nitrate. G. E. Patrick, in a n address on " T h e Detection of Thickeners in Ice Cream.* made before t h e 24th Annual Convention of Official Xgricultural Chemists, speaks of what is probably t h e same or a very similar decomposition product, often found in ice cream after i t has soured. H e is not certain as t o t h e exact nature of this substance, b u t believes i t t o be d u e t o t h e action of bacteria. H e finds t h a t this "pseudo-gelatin," as he calls it, forms a precipit a t e with picric acid similar t o t h a t formed b y gelatin under t h e same conditions a n d mentions t h a t there is no method known for distinguishing t h e one from t h e other. His suggestion, t h a t formaldehyde be added in t h e laboratory t o prevent t h e bacterial action which produces this decomposition product, is of course n o t applicable t o creams received sour. T h e picric acid precipitate from t h e sour cream is flocculent, resembling Al(OH)3 in form a n d settles quite rapidly, while t h a t due t o gelatin is small a n d granular, much like B a s 0 4 in form, settles very slowly a n d on shaking t h e test t u b e thoroughly will coalesce in large lumps leaving t h e solution almost clear. While these differences are quite \veil defined, t h e large n u mber of sour cream samples received in this laboratory made a method leaving less room for d o u b t , in t h e detection of even small amounts of gelatin, very desirable. After some experimenting I found t h a t there was a sharply defined difference between t h e solubilities of t h e t w o precipitates in hot, neutral water. While both precipitates are soluble on heating in slightly acid solutions, only t h e gelatin picrate is soluble in hot, neutral water alone. T h e picric acid precipitate from t h e sour cream is seemingly entirely insoluble i n hot water, after all t h e picric or other acid has been removed. T o I O cc. of t h e cream are added a n equal volume 1 U. S DPpt Agr , Bull. 107 (re\ 1, p 121. 2 U S Dept. A g r , Bull 116, p 24.