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UNITED STATES DEPARTMENT OF AGRICULTURE

Contribution aan the Bureau of Animal Industry . MELVIN, Chief

Washington, D. C. PROFESSIONAL PAPER June 29, 1916

COMPARISON OF THE BACTERIAL COUNT OF MILK WITH THE SEDIMENT OR DIRT TEST.

By H. C. CampBELt, Expert in Milk Hygiene, Pathological Division.

CONTENTS. Page, Page. Utility of the sediment test..........-..-..-. 1 | Details of the experiments—Continued: Obj ecitotibetworksse ssa. econ a se eens 2 Comparisons with unfiltered market milk 3 Outihneokexperiments-2--5 54-6 <=. 5-- 2-0-8 2 Comparisons with filtered milk.......... 5 Method of collecting samples,......---------- 3.-'| 3 CONCIUSIONS Bes er yaa tye nore eae 6: Deiails of the experiments..........-2=2---4- oral, eferencestopliteraturesnas=- eee ease eee 6

UTILITY OF THE SEDIMENT TEST.

The sediment or dirt test has been used for some time as a means of detecting visible dirt in milk. It was first applied in Europe to grade the milk as it arrived at the milk-receiving stations. After the milk had passed through the cotton disks they were cut in two, one part being kept for reference and the other mailed to the pro- ducer. In this manner it was found to be valuable in inducing the farmer to produce cleaner milk.

During the past few years the sediment test has gained great favor among milk inspectors in this country. They say it has been of great value, as they can actuallyshow the farmer when his milk is insanitary and in this way better fix a standard of prices at the milk-receiving stations. Until recently the grading of milk and cream at receiving stations was based entirely upon such tests as those for per cent of fat, acidity, odor, etc. No test was used whereby any information could be gained regarding the sanitary conditions under which the milk was produced.

Since the discovery of the sediment or dirt test the grading or judging of milk at receiving stations has been of two kinds, chemical and hygienic. It has been the opinion of inspectors that when milk contained sediment or dirt it was insanitary, but until the discovery

26052°—Bull. 361—16

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2 BULLETIN 361, U. S. DEPARTMENT OF AGRICULTURE.

of the sediment test they never had a means of quickly determining the exact amount. It has also been a fact long and fairly well estab- lished that milk contaiming sediment or visible dirt, such as manure, hair, etc., was produced under insanitary conditions, but when these ingredients were not present in the milk no field inspector could determine its purity.

Upon the adoption of the sediment test as a means of detecting insanitary milk at the milk-receiving stations, the producers un- doubtedly began to use methods calculated to remove the visible dirt. Such methods have been resorted to as straining the milk through cotton, cheesecloth, and Canton flannel to prevent the detection of visible dirt at the station by the field inspector. These methods have so changed the value of the sediment test as a means of judging pure milk that when no sediment or visible dirt can be detected it is often almost impossible to state whether the milk is produced under sanitary conditions or not. In order to determine whether the sediment test could be wholly relied upon as a means of detecting insanitary milk at milk-receiving stations, an experiment was conducted with this purpose in view.

OBJECT OF THE WORK.

The object of this experiment was to prove whether milk contain- ing little or no visible dirt, as often occurs when filtered through certain substances by gravity, was free from a large number of bac- teria. It was decided that by comparing the bacterial count with the sediment test (also when milk was filtered through various utensils) certain information could be obtained regarding “tile point.

OUTLINE OF EXPERIMENT.

Briefly, the experiment was conducted as follows:

Three of what we considered the most practical sediment-test apparatuses were used, namely, the Gerber, the Wizzard, and the Lorenz. The Gerber apparatus was selected because it represents a gravity method. The average length of time required for one pint of milk to pass through the disk by this method was 15 minutes. The Wizzard was selected as a pressure type which could be easily car- ried for field work and attached to the milk bottle without removing the milk. By this method the time required for the milk to pass through the disk was about two minutes; its disadvantage was that when the pressure was applied there was no means of holding the apparatus securely to the bottle. The Lorenz apparatus was se- lected as a pressure type in which the milk is placed in the metal container and the pressure applied. The time required by this

Bul. 361, U. S. Dept. of Agriculture PEATEs

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GOOD FAIR ~IEDIVU/NIT BAD

Fic. 1—CoTTON DiSKS SHOWING FOUR DEGREES OF SEDIMENT FROM MILK.

Fia. 2.—COMPARISON OF DISKS IN PAIRS RESULTING FROM THREE KINDS OF SEDIMENT TESTS.

BACTERIAL COUNT OF MILK AND DIRT TEST. 8

method was also about two minutes, and we found it to be the most satisfactory for field work.

Fifty samples of milk were collected on the railroad station plat- form from milk cans as they arrived from various farmers throughout the section. Upon arrival at the laboratory the temperature was taken and a bacterial count made. After preparing plates each sample was passed through one of Gerber’s sediment tubes. The sediment disks were kept and compared with the bacterial count. A similar comparison was also made with the Wizzard and Lorenz apparatuses, using 50 samples in each case.

After 50 samples had been tested with each apparatus, 20 samples were filtered through 4 pieces of cheesecloth, 20 through one thick- ness of absorbent cotton, and 20 through one of Canton flannel. Each of these samples was then subjected to the sediment test and a bacterial count made in each case; this was done to determine the effect that straining the milk would have upon the test. We also made a comparison of the filtered samples with the bacterial count after passing them through the cotton disks used in the Lorenz apparatus.

The writer wishes to thank Dr. John R. Mohler, assistant chief of the Bureau of Animal Industry; Dr. Louis A. Klein, dean of the veterinary school, University of Pennsylvania; and Dr. C.J. Marshall, State veterinarian of Pennsylvania, for many valuable suggestions in the work.

METHOD OF COLLECTING SAMPLES.

The milk in the can was thoroughly shaken and 1 pint taken as a sample. The sediment in this kind of sample would, in our opinion, represent the amount of dirt contained in an ordinary bottle of milk. A few inspectors believe that the sample should be collected from the bottom of the cans before shaking, but it seems to us that this may at times be unfair to the producer.

DETAILS OF THE EXPERIMENTS.

In our experiments the character and quantity of sediment upon the cotton disks is represented by the words ‘‘good,” “fair,” ‘‘me- dium,”’ and ‘‘bad.”’ (Pl. I, fig. 1.) This gives four classifications, which we considered sufficient for all practical purposes. These

classifications are illustrated in Plate I. COMPARISONS WITH UNFILTERED MARKET MILK.

Table 1 shows the laboratory results obtained by comparing the bacterial count with the Gerber sediment test on 10 average samples out of 50.

4 BULLETIN 361, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 1.—Comparison of bacterial count with Gerber sediment test (unfiltered market milk).

Character |

| Bacteria Bacteria = : + : Character Sample No. per cubic : Sample No. per cubic . ‘centimeter. | /Sediment. centimeter. |°! Sediment. SSS SS 1 eR Oa | 2,690,000 | Fair. || elidel Allg 1,206,000 | Fair. DR ies kth a3 3 ee ee 128127 000 «| Medinm-o pilez?.. S<ebrete. as nee 108,000 | Bad. Bete Cac d ae ee eee 1,537,000 | Good. 1 eke yieaie terre Serene: a SER 263,000 | Good. A a Sn eee EES Lea | 186,000 | Bad. HOR Slee. Se Ns fore 2 eee 1,803,000 | Fair. to os eae eee ae | 643,000 | Medium. | LORE ee Mea ae eee 319,000 | Medium

In these results it will be seen that some samples had a high bac- terial count, yet tested ‘‘good”’ or ‘‘fair’’ with the sediment test, while others which had a low bacterial count tested ‘‘medium” or So pace.

Plate I, figure 2 (upper), shows two of the samples—No.7 and No. 1. No. 7, having a large amount of sediment and classed as ‘‘bad,” has a low bacterial count, while the other, No. 1, is classed as ‘‘fair,’’ and has a high bacterial count.

Table 2 shows the tabulated results obtained by comparing the bacterial count with the Wizzard sediment test on 10 average sam- ples out of the 50.

TaBLe 2.—Comparison of bacterial count with Wizzard sediment test (unfiltered market

milk). Bacteria Bacteria < : Character + : Character Sample No. per cubic F | Sample No. per cubic . centimeter. | Sediment. | centimeter. |! Sediment.

It will be seen here that a greater difference occurred than in the

preceding table.

Plate I, figure 2 (middle) shows disk No. 8, classed as ‘‘ good,” con- taining 4,102,000 bacteria per cubic centimeter, while disk No. 10, classed as ‘‘bad,”’ contained only 243,000 per cubic centimeter.

Table 3 shows the tabulated results obtained by comparing the bacterial count with the Lorenz sediment test on 10 average samples

out of 50.

TABLE 3.—Comparison of bacterial count with Lorenz sediment test (unfiltered market

Sample No.

ee er eee

Bacteria per cubic centimeter.

768, 000 99, 000 63, 000 57,000 34, 000

milk). Character of sediment. Sample No. Fair. Oh Hae bee a bree et Be Good. esse A EES diye Sle OO the Sih Bad. phar Ut age NM oie se Woes Bee tome Do. LS pe ee ius oi Do. 1 | EA ne patna gen ee ee Bah he Bie oe

Bacteria per cubic centimeter.

329, 000

Character of sediment.

BACTERIAL COUNT OF MILK AND DIRT TEST. 5

This table, like the others, shows considerable variations; No. 1, which had a bacterial count of 768,000, tested ‘‘fair’”’ by the sediment test, and No. 8, which has a count of 7,200, tested ‘‘bad.’’ These disks are shown in Plate II (lower).

COMPARISONS WITH FILTERED MILK.

After comparing the bacterial count with the various sediment tests of unfiltered market milk, it was decided to make a comparison after the milk was filtered through such substances as are frequently used as strainers by farmers to remove dirt. Twenty samples were filtered through 4-ply cheesecloth and the Lorenz disks compared with the bacterial count.

_ The table below shows the results obtained from 10 average samples out of 20; filtering through cheesecloth.

TaBLE 4.—Comparison of bacterial count with Lorenz sediment test (milk filtered through

cheesecloth). Bacteria Bacteria : Character = : Cheracter Sample No. sper cubic | of sediment. Sample No. sper cubic |ofsediment. Da ORaee Bee Eee Nee aaee 109,000 | Good. Seaweed See 33,000 | Good Disa jue hE ROTEL Tea eS 67,000 | Do. Toate. SEPOL EE ISS 84,000 | Do Rn eee oe a el eee 46, 000 Do Se Soles Soe neie ap ieee 93, 000 Do MCAERI SS: SAGER ST baer» 2: 24,000 Do OVS Rays eee. 1 54, 000 Do DS Soy a Se CCI CE er ees 639, 000 Do Loe ee ee a ee 316, 000 Do

Twenty samples were filtered through one ply of Canton flannel and the bacterial count compared with the Lorenz disks. Table 5 shows the results obtained from 10 average samples out of 20.

TaBLE 5.—Comparison of bacterial count with Lorenz sediment test (milk filtered through 1-ply Canton flannel).

Bacteria Bacteria : Character + : Character Sample No. er cubic : Sample No. er cubic i P centimeter. ofsediment. P Guntinietas ofsediment. 1 See ee es ee 78,000 | Good RNS Oe Ls SRLS OLS te eee | 19,400 | Good Nas ie ARDS c Bill oy pe eae eg aE 31, 000 Do. UseGAk Ske See sae eae 316, 000 Do. os ene Vn 41, 000 Do. Seen ret re tee ae 129, 000 Do. 7 ony Ack 0 Rea eee pore oe 108, 000 Do. Oral Pek Ree Rey ee 149, 000 Do. Fil SS ea eee 18,000 | Do. UD Ea sac es eae ald 119,000} Do.

Twenty samples were filtered through 1-ply ordinary absorbent cotton, covered above and below with 1-ply cheesecloth. The Lorenz disks were compared with the bacterial count, as in the preceding

table. out of 20.

Table 6 shows the results obtained from 10 average samples

6 BULLETIN 561, U. S. DEPARTMENT OF AGRICULTURE.

TABLE 6.—Comparison of bacterial count with Lorenz sediment test (milk filtered through 1-ply absorbent cotton and cheesecloth).

Bacteria Bacteria

= - | Character = : Character

Sample No. see eee of sediment. Sample No. oe i sediment. 1 Sree ae on ea 760,000 | Good. WO ices aoe ates eee | 57,000 | Good PEI EL ead ie ee era 67, 000 Do. Wiss coche leneaes oso wears 362, 000 Do GERI ST or Se 5 ae 31, 400 Do | its eee ae Gris eee picts afd an Se 471, 000 Do Agee ee renee nen Fr TLL, 42,000 Do. eae 2224 SSE ae eee 48, 000 Do GE, ele CS wees 61, 300 Do. 113K) Seon atest s £ Fite sa eet cit 191, 000 Do

J }

In every instance in which the milk was filtered through any sub- stances to remove visible dirt the disks were classed as good.

It would seem from the results shown in the last three tables that if milk is strained before applying the sediment test the latter is of little, if any, value in estimating visible dirt.

CONCLUSIONS.

1. The writer considers the Lorenz apparatus the most convenient and practical for demonstrating dirt in milk.

2. The quantity of sediment or visible dirt present on the disk is no criterion as to the kind or number of bacteria contained in the milk.

3. The various sediment tests are applicable only in roughly esti- mating the quantity of sediment in unstrained milk, and can not be used solely as a means of determining the hygenic conditions under which it was produced.

4. If milk is strained through the substances mentioned, the sedi- ment testers are of little value in estimating the degree of contami- nation. | = REFERENCES TO LITERATURE.

New and Improved Tests of Dairy Products. S. M. Babcockand E. H. Farrington, Wisconsin Station Bulletin No. 195, pp. 3-13.

The Milk Sediment Test and Its Application. A.C. Baer, Wisconsin Agricultural Experiment Station, Circular of Information No. 41.

Experiment with Fhlegel’s Apparatus for Determining Dirt in Milk. J. Klein, Milchw. Centbl. 1. (1905), No. 7, pp. 305-307.

Comparison of Bacteria in Strained and Unstrained Samples of Milk. H. W. Conn and W. A. Stocking, Storrs Agricultural Experiment Station Bulletin, 1903-1905.

PUBLICATIONS OF U. S. DEPARTMENT OF AGRICULTURE RELATING TO BACTERIAL CONTENT OF MILE.

AVAILABLE FOR FREE DISTRIBUTION.

A Bacteriological Study of Retail Ice Cream (Department Bulletin 303). The Present Status of the Pasteurization of Milk (Department Bulletin 342). Care of Food in the Home (Farmers’ Bulletin 375).

The Care of Milk and its Use in the Home (Farmers’ Bulletin 413).

Bacteria in Milk (Farmers’ Bulletin 490).

Production of Clean Milk (Farmers’ Bulletin 602).

FOR SALE BY THE SUPERINTENDENT OF DOCUMENTS, GOVERNMENT PRINTING OFFICE, WASHINGTON, D. C.

The Alcohol Test in Relation to Milk (Department Bulletin 202). Price, 5 cents.

Pasteurizing Milk in Bottles and Bottling Hot Milk Pasteurized in Bulk (Department Bulletin 240). Price, 5 cents.

Relation of Bacteria to the Flavors of Cheddar Cheese (Bureau of Animal Industry Bulletin 62). Price, 5 cents.

The Bacteria of Pasteurized and Unpasteurized Milk under Laboratory Conditions (Bureau of Animal Industry Bulletin 73). Price, 5 cents.

The Milking Machine asa Factor in Dairying, Preliminary Report: 1, Practical Studies of a Milking Machine; 2, Bacteriological Studies of a Milking Machine (Bureau of Animal Industry Bulletin 92). Price, 15 cents.

_ The Bacteriology of Cheddar Cheese (Bureau of Animal Industry Bulletin 150). Price, 10 cents.

Methods of Classifying the Lactic-acid Bacteria (Bureau of Animal Industry Bulletin 154). Price, 5 cents.

A Study of the Bacteria Which Survive Pasteurization (Bureau of Animal Industry Bulletin 161). Price, 10 cents.

Bacteria in Milk (Separate 444 from Yearbook 1907). Price, 5 cents.

ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT

5 CENTS PER COPY

WASHINGTON : GOVERNMENT PRINTING OFFICE : 1916

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