Direct Microscopic

Question 1

What does the direct microscopic method allow analysts to examine in milk?

Answer 1

Numbers of bacterial clumps or somatic cells

This method is also known as the direct microscopic clump (DMC) count.

Question 2

What can be evaluated simultaneously with the counting of bacterial clumps?

Answer 2

Morphology and arrangement of bacteria

This evaluation helps identify quality problems.

Question 3

What do large numbers of bacterial clumps indicate?

Answer 3

Mastitis or other abnormal conditions of the udder

This is a significant indicator of udder health.

Question 4

What term has come to replace ‘leucocytes’ in the context of somatic cells?

Answer 4

Somatic cells

This change reflects a more meaningful expression of body cells associated with the udder.

Question 5

What is the official term for the microscopic method that counts somatic cells?

Answer 5

Direct microscopic somatic cell count (DMSCC)

This method is recognized for its research findings and application.

Question 6

How were somatic cell counts previously estimated before the DMSCC?

Answer 6

By one of several other testing methods

These previous methods were less direct than the current microscopic approach.

Question 7

What is the primary limitation of the direct microscopic method in pasteurized milk?

Answer 7

It is not used to determine compliance with finished standards

This is due to the generally low numbers of bacteria in pasteurized milk.

Question 8

Why might the direct microscopic method still be useful in quality control?

Answer 8

Large numbers of bacteria in uncultured milk indicate unsanitary conditions

This applies regardless of whether the bacteria are viable.

Question 9

Fill in the blank: The direct microscopic clump count is used to assess the _______ of milk.

Answer 9

Quality

This assessment can help identify potential health issues in dairy cows.

Question 10

What does DMC stand for in the context of milk analysis?

Answer 10

Direct Microscopic Count

DMC is used to evaluate the bacterial contamination of raw milk or cream samples.

Question 11

What is the primary purpose of evaluating the morphology of cells in milk samples?

Answer 11

To suggest the causes of high bacterial counts

This evaluation includes assessing the configuration of clumps and the presence of somatic cells.

Question 12

True or False: Most dry milk contains a high number of viable bacteria.

Answer 12

False

Most dry milk contains relatively few viable bacteria.

Question 13

What can microscopic examination of reconstituted dry milk samples provide?

Answer 13

Meaningful information on the previous sanitary history of the product

This examination can serve as a quality control measure.

Question 14

What is the relative standard deviation (RSDR) in counts made on the same sample of milk?

Answer 14

3.7

This indicates potential for wide interlaboratory differences.

Question 15

Fill in the blank: The number of somatic cells in raw milk provides a measure of the presence and extent of _______.

Answer 15

mastitis

Somatic cell counts help assess one aspect of raw milk quality.

Question 16

What are the two types of counts mentioned in the context of milk analysis?

Answer 16

• Direct Microscopic Counts
• Direct Microscopic Somatic Cell Counts

These counts measure bacteria and somatic cells per milliliter or gram of dairy product.

Question 17

What is the principle behind direct microscopic counts?

Answer 17

Bacteria or somatic cells are transferred to a slide, stained, and counted

This yields the number of cells per milliliter or gram of dairy product.

Question 18

What type of immersion oil is preferred for microscopy in this context?

Answer 18

Type B (medium viscosity)

The refractive index should be 1.51 to 1.52 at 20°C.

Question 19

What is the significance of using clear glass slides with etched surfaces?

Answer 19

They allow for confirmation of the correct reading area during analysis

This is important for achieving high accuracy.

Question 20

How should slides be cleaned for repeated use?

Answer 20

Submerge in hot detergent solution and rinse thoroughly

Alternatively, use appropriate commercial alkaline and/or acid cleaners.

Question 21

What instrument is mentioned for transferring 0.01-mL quantities?

Answer 21

Metal syringe

This instrument allows for rapid and convenient transfer but can create artifacts in milk films.

Question 22

What should be done immediately after using a metal syringe?

Answer 22

Disassemble and clean the measuring tube and piston

This prevents residues from drying on the instrument.

Question 23

What should be avoided when cleaning the syringe barrel and finger grip?

Answer 23

Do not submerge in detergents or solvents.

Proper maintenance prevents contamination and artifacts.

Question 24

How should the interior of a syringe be cleaned?

Answer 24

Use forced suction or pressure with a rubber bulb and soapless detergent, then rinse with clean water and air-dry.

Acids, alkalis, and ordinary soap solutions should not be used.

Question 25

What pH level should chemical cleaners be at when used for syringes?

Answer 25

At or near pH 7.0. ## Footnote This ensures compatibility and safety for the syringe materials.

Question 26

What is the first step before reassembling a syringe?

Answer 26

Ensure all detergent and milk residues are removed. ## Footnote Proper cleaning is crucial for accurate results.

Question 27

What precaution should be taken regarding syringe parts?

Answer 27

Do not interchange parts from one syringe with parts from another. ## Footnote This prevents compatibility issues and maintains accuracy.

Question 28

How often should syringes be tested for accuracy?

Answer 28

Annually. ## Footnote Certification may be required by regulatory agencies.

Question 29

What should be done if a syringe does not conform to specified milk deliveries?

Answer 29

Replace the syringe. ## Footnote Ensures reliability in measurements.

Question 30

How is the calibration of the volumetric load of a syringe determined?

Answer 30

By weight measurements of a representative test charge of milk. ## Footnote This method ensures precision in delivery.

Question 31

What is the average weight difference expected in a correctly calibrated syringe after multiple weighings?

Answer 31

0.0103 + 0.0005 g. ## Footnote This value indicates proper calibration.

Question 32

What are micro pipeters used for?

Answer 32

Measuring the 0.01-mL milk test portion. ## Footnote They are preferred instruments due to their precision.

Question 33

What is the purpose of a bent-point needle in milk testing?

Answer 33

Used for spreading milk or cream over a square centimeter area. ## Footnote This facilitates even distribution for analysis.

Question 34

What temperature range is recommended for drying films?

Answer 34

40° to 45°C. ## Footnote Uniform heat distribution is important for consistent results.

Question 35

What type of microscope is preferred for milk analysis?

Answer 35

A binocular microscope with a 1.8-mm oil-immersion objective. ## Footnote Additional features include an Abbe condenser and a numerical aperture of 1.25 or higher.

Question 36

What is the recommended magnification for oculars in milk testing microscopes?

Answer 36

10x magnification is recommended, with 12.5x to 15x permitted. ## Footnote This ensures sufficient detail for analysis.

Question 37

What is the significance of the microscopic factor (MF) in milk analysis?

Answer 37

It determines the amount of milk that can be examined in any one field. ## Footnote MFs are used to calculate bacterial clumps or somatic cells per field.

Question 38

What should be ensured about the surface for drying films?

Answer 38

It should be clean, dust-free, and level. ## Footnote A regulated heat source is also necessary.

Question 39

Fill in the blank: Syringes should be cleaned before _______.

Answer 39

first use.

Question 40

True or False: It is acceptable to use ordinary soap solutions for cleaning syringes.

Answer 40

False. ## Footnote Ordinary soap solutions can damage the syringe.

Question 41

What should be adjusted for individuals using paired oculars in microscopy?

Answer 41

Diaphragms must be specially adjusted for the individual ## Footnote Counts must be corrected based on the diameter of the field observed.

Question 42

What is the significance of constant tube length in microscopes?

Answer 42

It keeps the resultant calibrated field and magnification constant regardless of changes in interpupillary settings.

Question 43

What is the MF in microscopy?

Answer 43

Magnification Factor ## Footnote It is calculated based on the field diameter observed.

Question 44

How is the Magnification Factor (MF) calculated?

Answer 44

MF = 3.1416 x d² / 40,000 ## Footnote 'd' is the diameter measured under the oil-immersion objective.

Question 45

What is the formula to express the MF?

Answer 45

Express the MF to 2 significant figures.

Question 46

What does the reciprocal of the MF represent?

Answer 46

The fraction of 1 mL of milk observed in 1 microscopic field.

Question 47

What is the purpose of the ocular disc in microscopy?

Answer 47

To subdivide the field for counting purposes.

Question 48

What type of stage is required for microscopy?

Answer 48

A regular mechanical stage or a special stage for specific slide sizes.

Question 49

What is a stage micrometer slide used for?

Answer 49

To measure field diameter accurately.

Question 50

What is a hand tally used for in microscopy?

Answer 50

To count cells or particles observed.

Question 51

At what temperature should samples be warmed before testing for DMSCC?

Answer 51

40°C.

Question 52

How should samples be mixed before preparing films?

Answer 52

Shake 25 times in 7 seconds with a 1-foot movement.

Question 53

What is the maximum time to allow foam to disperse after mixing?

Answer 53

No more than 3 minutes.

Question 54

What is essential for cleanliness when preparing films?

Answer 54

Instruments and glassware must be scrupulously clean.

Question 55

What is the drying temperature range for films?

Answer 55

40° to 45°C.

Question 56

What should be done with the measuring tube before each use?

Answer 56

Rinse it in fresh tap water.

Question 57

What is the correct technique for using a 0.01-mL syringe?

Answer 57

Dip the tip slightly below the surface and repeatedly draw in and expel water.

Question 58

What should be avoided when wiping the tip of the syringe?

Answer 58

Do not wipe over the tip.

Question 59

What is the procedure for using micro pipeters?

Answer 59

Use a separate tip for each sample and avoid foam.

Question 60

What should be done with used tips from micro pipeters?

Answer 60

Discharge into disinfectant or biohazard bags.

Question 61

What is a key consideration during film preparation to prevent contamination?

Answer 61

Protect films from exposure to dirt, dust, and insects.

Question 62

What should be done with a clean bent-point dissecting needle between samples?

Answer 62

Wipe the needle on a clean, dry tissue or towel

Question 63

At what temperature should the milk film be dried?

Answer 63

40° to 45°C

Question 64

What is the recommended method for handling multiple slides during staining?

Answer 64

Use holders of glass, stainless steel, or other suitable material

Question 65

What should be avoided when preparing stains?

Answer 65

Using liquid reagents that contain suspended foreign matter

Question 66

Which three stains may be used for cow's milk?

Answer 66

* LW/NL-T stain * LW/NL-X stain * LW/NL-F stain

Question 67

What is the issue with the LW/NL-T stain when used for goat's milk?

Answer 67

It has produced highly variable results and is unreliable for somatic cell count

Question 68

What is a suitable replacement for staining somatic cells in goat's milk?

Answer 68

Pyronin Y methyl green stain with Carnoy's fixative

Question 69

What are the components for the LW/NL-T stain?

Answer 69

* 0.6 g of certified methylene blue chloride * 52 mL of 95% ethyl alcohol * 44 mL of tetrachlorethane * 4 mL of glacial acetic acid

Question 70

How long should the LW/NL-T stain solution stand?

Answer 70

12 to 24 hours at 44° to 72°C

Question 71

What is the difference in the preparation of LW/NL-X stain compared to LW/NL-T stain?

Answer 71

LW/NL-X uses xylene instead of tetrachlorethane and 0.5 g of methylene blue chloride

Question 72

What is included in the Canadian modification of the modified Newman-Lampert stain?

Answer 72

Basic fuchsin dye

Question 73

What are the components for Carnoy's fixative?

Answer 73

* 60 mL of chloroform * 20 mL of glacial acetic acid * 120 mL of 100% ethyl alcohol

Question 74

What should be done with the pyronin Y stain before use?

Answer 74

Filter through Whatman No. 1 paper

Question 75

How should dried, stained slides be rinsed after staining?

Answer 75

In 3 changes of tap water at 35° to 45°C

Question 76

What is the requirement for the New York modification of the pyronin Y-methyl green stain procedure?

Answer 76

Use of a fume hood

Question 77

How long should a prepared film be fixed in Carnoy's fixative?

Answer 77

5 minutes

Question 78

What should be done with used staining solutions?

Answer 78

Discard them whenever they become contaminated or unsuitable

Question 79

How should slides be stored after examination?

Answer 79

In dust-free, slide-storage boxes

Question 80

What can interfere with the staining procedure or future re-examination of milk films?

Answer 80

Accumulation of pencil marks on slides

Question 81

What is the criteria for counting bacteria in separate clumps?

Answer 81

Count as separate clumps if 2 cells or clumps are separated by a distance equal to or greater than twice the smallest diameter of the 2 cells nearest each other.

Question 82

What cells are counted in DMSCCs?

Answer 82

Only somatic cells with an identifiable stained nucleus.

Question 83

What color is the stained nucleus in bovine somatic cells?

Answer 83

Dark blue.

Question 84

What color is the stained nucleus in caprine somatic cells?

Answer 84

Blue or blue-green.

Question 85

How do you count polymorphonucleated cells?

Answer 85

Count as a single cell if it has two or more discernible nuclear lobes.

Question 86

What is the minimum diameter for a nucleus to be counted?

Answer 86

8 microns.

Question 87

What is the formula to calculate the area of a single strip in the counting method?

Answer 87

Area of a single strip (mm²) = 11.28 mm x D (in mm).

Question 88

How do you determine the number of single strips in a 0.01-mL milk film?

Answer 88

Number of single strips = 100 mm² / area of single strip.

Question 89

What is the Single Strip Factor (SSF)?

Answer 89

SSF = Number of strips in 0.01 mL x 100.

Question 90

What is the counting procedure for a single-strip count?

Answer 90

Focus on the film edge, traverse the diameter, counting cells within the strip and those touching one edge.

Question 91

How is the count per milliliter calculated?

Answer 91

Count per milliliter = Number of somatic cells and/or bacterial clumps in a single strip x SSF.

Question 92

What is the importance of analyst training in counting accuracy?

Answer 92

The training and skill of the analysts are crucial for accuracy, precision, and reproducibility.

Question 93

What are some factors responsible for variations in counts?

Answer 93

* Inaccuracy in measuring samples * Faulty preparation and staining * Minute amount of milk examined * Irregular distribution of cells * Poor microscopy * Eye fatigue * Analyst inexperience.

Question 94

How should counts be reported?

Answer 94

Report counts only to the first 2 left-hand digits of the estimate, followed by the appropriate number of zeroes.

Question 95

What is the rule for rounding when the third digit is 5?

Answer 95

If the second digit is odd, round up; if even, round down.

Question 96

What should be done with slides that have violative counts?

Answer 96

Save slides for future reference.