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continued just as quickly as at the farm where it was discarded. Both farms occasionally brought milk containing many streptococci during the year that followed.

No systematic studies of the streptococci have been made, and all cocci tending to grow in chains including more than four to six individuals have been included in this group. It is therefore probable that a variety of types or species are included under this term.

A lookout has been maintained for other abundant organisms derived from the udder but none have been detected except in one instance. The organism in this case was a tiny micrococcus which was traced back to the udder of a single animal in a small herd. This animal was giving milk of a normal appearance but was not a profitable animal and was sold before an opportunity was presented to study the matter further.

The failure to find organisms which might be identified with the tubercle organism, or other organisms which have been described as occurring in the udder in large numbers was surprising. This negative result may mean little, however, as small numbers of any of these organisms might have been overlooked, and large numbers may occur but rarely. It is possible, moreover, that a careful identification of the organisms in the microscopic preparations would have permitted the recognition of some of these organisms.

The result of these attempts to recognize the causes of the highcount milk has been to indicate that the three things which have just been discussed (improperly cleaned milk cans, improperly cared for milking machines, and streptococcic udder infections) have caused nearly all of the high germ counts which were due to initial contamination of the milk. This includes nearly all of the milk examined, as conditions favorable to an extensive growth of the organisms in the milk were uncommon. Even the night milk was only twelve to sixteen hours old when examined and in the majority of cases was cooled below 60° F.

Of the 11,851 samples considered 643 were examined by the plate method as well as by the microscopic method.15 Out of this number 518 samples showed fewer than 1,000,000 bacteria per c. c. by the microscopic method and less than 200,000 colonies per c. c. by the plate method; fifty-eight samples showed more than 1,000,000

15 See footnote 7.

and less than 10,000,000 bacteria by the microscopic method and at the same time a plate count in excess of 200,000 and less than 1,500,000 per c. c.; while eleven samples showed more than 10,000,000 bacteria per c. c. and at the same time gave a plate count in excess of 1,500,000 per c. c. In other words, if we accept the limits set as marking the limits between A, B and C milk, there was an agreement in the ratings given these samples in 587 cases out of 643 (91.29 per ct.).

The discrepancies in ratings were grouped as follows: 24 samples of milk which were rated as "good" by the microscopic method were rated as grade B by the plate method; likewise 24 samples of milk which were rated as "medium" by the microscopic method were rated as grade A by the plate method. Eight samples were rated as "medium" by the microscopic method which were classed as grade C by the plate method. The latter type of discrepancies, as already explained (p. 252), was due to the fact that the 10,000,000 limit used in the case of the microscopic method is more lenient than the 1,500,000 limit used in the case of the plate method.

Attention should be called to the fact that the agar-plates used in making these counts were incubated for five days at 21° C. followed by an incubation of two days at 37° C., so that the counts obtained were in all probability higher than they would have been if the plates had been incubated according to the procedure ordinarily used in routine work, namely, two days at 37° C.

Table III gives the results secured during a seven-day period in August, 1915, during which time each can of milk received at one of the two companies was sampled. Table IV gives similar results from samples taken at the same milk station during a seven-day period in February, 1916, while Table V gives a summary of the results in Tables IV and V. Between 33 and 51 samples were taken per day. The work of preparing materials, collecting and examining all of the 574 samples was done by the junior author (Bw.) and did not prove an especially burdensome task. All results were ready soon after noon of the day on which the samples were taken.

The chief purpose in taking these samples was to learn whether a reasonably accurate judgment was secured in regard to the quality of the milk brought by an individual dairyman when samples were taken on one day per week. The results showed that during the

August period there were only four of the seventeen dairymen who brought milk of such quality that all cans graded "good." In the winter time (February), this number was increased so that all but three of the seventeen brought milk, all of which graded "good." In the case of these men it is evident that it made no difference how many samples were taken, as the rating for the week would have been the same regardless of the number of samples taken.

The fact that it is necessary to take samples of both morning and night milk in order to get a fair estimate of the quality of milk brought is shown by the summary (Table V) as well as by many individual instances (Tables III and IV). The night milk being twelve to sixteen hours old naturally more frequently falls into the "medium" and "poor" classes than does the morning milk. Thus in the winter time only three "medium" cans appeared in the morning milk, while there were ten cans of night milk which graded "medium." The contrast between the night and morning milk was still more striking in the summer months where there were forty-one cans of "medium" milk and four cans of "poor" milk in the night milk as contrasted with only eleven cans of “medium" and none of "poor" morning milk. From these findings, it is evident that if samples had been taken from night milk only for use as a basis of payment to the dairymen, the ratings given would have been more severe than were warranted. This injustice would have been worse in the summer months than in the winter time.

The surprisingly great variation in the quality of the milk found in some instances in different cans of milk as delivered by the same dairyman on the same or different days makes it evident that it is no easy matter to sample the milk delivered in such a way as to secure a reasonably accurate grading. The difficulties involved are far greater than those involved in getting an accurate butterfat test.

It was disappointing to find that because of the highly variable conditions the records secured were neither detailed enough nor extensive enough to permit a satisfactory mathematical analysis of the results. If commercial use is to be made of the bacterial count in the buying and selling of milk, it is highly important that studies be made to determine how many samples should be taken each week in order to secure reasonably accurate results.

TABLE III.- GRADES GIVEN THE INDIVIDUAL CANS OF MILK RECEIVED AT A MILK STATION DURING A SEVEN-DAY PERIOD IN AUGUST.

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* It was usually possible to recognize which was night milk and which was morning milk from the temperature, as the morning milk was not cooled. It was evident that morning and night milk were mixed in certain cases.

† Each single letter represents a can of milk. G signifies less than 1,000,000 bacteria per c. c., M more than 1,000,000 and less than 10,000,000, and P more than 10,000,000.

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TABLE IV.- GRADES GIVEN THE INDIVIDUAL CANS OF MILK REceived at A MILK STATION DURING A SEVEN-DAY PERIOD IN FEBRUARY.

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*It was usually possible to recognize which was night milk and which was morning milk from the temperature, as the morning milk was not cooled. It was evident that morning and night milk were mixed in certain cases.

† Each single letter represents a can of milk. G signifies less than 1,000,000 bacteria per c. c., M more than 1,000,000 and less than 10,000,000, and P more than 10,000,000.

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