Historic, archived document Do not assume content reflects current scientific knowledge, policies, or practices. pei ea, ee 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 | : 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 = oo = ae 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 Deeper Gast Sas. to TOIT ee eos) Ue a pee ABET eee Pants _ - - 7 . 7 « : _ i i - " Sans. —_ ae o & ae - ae my, tees . : ‘(PET UM Wt At? 3253 307-3 42 : Pies. Sa ; . a ; = - ae ae ~h = } bh r - 7 sa - @ y * > _ - , : 5 oe a in i FE Mi * «. - = = r ‘ % nah * ig ra : . ‘ < - . . — = we a j « 2 7 ee E . } a + ~ >: ~ 2 s m = 4 a r = = ; a z . ca * 7~ = . ‘ > . ~* ~ - ‘ P = Pe - ”