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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 


= 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<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. 

De se es cn ere 2,131,000 | Fair. HG eae cra tee ee 246, Bad. 
Os Bart iy Heenan 622,000 | Good. 7a cee ge ee 3,558,000 | Fair. 
Be Fs ties eee .1,391, 000 Do. Sdeie ohutteal Fes Leer 4,102,000 | Good. 
ee esos eens 812,000 | Bad. Gere see oe 5 eee terete 2,688,000 | Fair. 
Den ges tees. Saas 377,000 Do. PB 02 ee 8 Ee eats ie Ne eee 3,000 | Bad. 


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 
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_ The Bacteriology of Cheddar Cheese (Bureau of Animal Industry Bulletin 150). Price, 
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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 
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Bacteria in Milk (Separate 444 from Yearbook 1907). Price, 5 cents. 


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