The inability to thoroughly render vessels bacteria-free with the conveniences which are generally to be found on the farm has led in some cases to the custom of washing and sterilizing the milk cans at the factory.
Germ content of milk utensils. Naturally the number of bacteria found in different milk utensils after they have received their regular cleaning will be subject to great fluctuations; but, nevertheless, such determinations are of value as giving a scientific foundation for practical methods of improvement. The following studies may serve to indicate the relative importance of the utensils as a factor in milk contamination.
Two cans were taken, one of which had been cleaned in the ordinary way, while the other was sterilized by steaming. Before milking, the udder was thoroughly cleaned and special precautions taken to avoid raising of dust; the fore milk was rejected. Milk drawn into these two cans showed the following germ content:
| No. bacteria per cc. | Hours before souring. | |
| Steamed pail | 165 | 28-1/2 |
| Ordinary pail | 426 | 523 |
Harrison[6] has shown how great a variation is in the bacterial content in milk cans. The utensils were rinsed with 100 cc. of sterile water and numerical determinations of this rinsing water made. In poorly cleaned cans, the average germ content was 442,000; in cans washed in tepid water and then scalded—the best farm practice—54,000, and in cans carefully washed and then steamed for five minutes, 880.
Another method used by the writer is to wash the utensil with 100 cc. sterile wash water, using a sterile swab to remove dirt. Then repeat the process twice or more with fresh rinsing waters, making plate cultures from each. The following data were obtained from three such determinations:
| No. bacteria in different washings. | |||
| I. | II. | III. | Total No. bacteria. |
| 7,800,000 | 1,450,000 | 49,000 | 9,299,000 |
| 283,000 | 43,400 | 35,000 | 361,400 |
| 1,685,000 | 105,000 | 61,400 | 1,851,400 |
Infection of milk in udder cavity. A frequently neglected but considerable factor of infection is that which is attributable to the bacteria which are present in the udder and which are removed in large numbers during the milking process. An examination of the fore milk, i. e., the first few streams from each teat, and that which is subsequently withdrawn, generally reveals a very much larger number of organisms in the fore milk.[7] Not infrequently will this part of the milk when drawn under as careful conditions as possible, contain several score thousand organisms per cc. If successive bacterial determinations are made at different periods of the milking, as shown in the following experiment, a marked diminution is to be noted after the first portion of the milk is removed: