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Summary Observations on the production of animals before and after the development of laboratory evidence of mastitis were made. These data are derived from animals in the early stages of infection and animals in which the disease was latent in character. In many cases no clinical evidence was observable during most of the mastitis reacting periods. Since animals showing obvious clinical evidence of mastitis were eliminated from the herds as a matter of routine practice before the full impact of chronic mastitis on production of milk was manifested, it is evident that the full adverse effect on yield is not here measured. Rather, these data tend to show that a loss in yield may occur in the majority of cases during the incipient stage of the disease. In 240-day lactations of a group of 30 cows having a history both as mastitis free and mastitis positive based on the bromthymol blue test, the sediment test, the leucocyte count, and the shedding of organisms, there was a loss of 463 pounds of milk attributable to mastitis. In another herd of 22 cows there was a loss in yield of 425 pounds. These reductions are between 4 and 5 per cent and are not particularly significant. A loss in yield was manifested in about two thirds of the individual cases. When only one quarter was positive there was no loss in yield. Such are usually incipient stages, and possibly also compensation in yield is made by the unaffected quarters. The loss, however, increased in magnitude with each additional quarter involved amounting to about 15–20 per cent with all four quarters positive. When the results were segregated for each diagnostic test it was found that for those reacting to the bromthymol blue test the loss in yield was 837 pounds, and for those shedding S. mastiditis the loss amounted to 1100 pounds per lactation. The loss in yield of sediment positives was 596 pounds and of leucocyte positives 573 pounds. No effect on the butterfat percentage was observed.

Summary Observations on the incidence of streptococcal mastitis in seven experimental herds over periods of from one to six years are described. Data collected before and after the adoption of a program of segregation based on periodic examinations (chiefly bacteriological) and segregation of animals shedding streptococci identified as Streptococcus mastitidis (Group A) * are presented. The results obtained indicate that: 1.The annual rate of spread of infectious streptococcal mastitis in infected herds may be reduced from 50 to 100 per cent by the use of the segregation plan described in this paper and in a previous publication (1). 2.While the rate of spread of infection is materially reduced by segregating infected animals at one end of the milking string and milking them last, complete separation is necessary to entirely prevent the spread of infection. 3.Herds free from Streptococcus mastitidis (Group A) may be established by segregation of the normal animals, disposal of infected individuals, and replacement by first calf heifers that have not been exposed to infection following parturition. The results presented support the opinion that it is possible to establish and maintain a herd free from the organism generally recognized as Streptococcus agalactiae . The writers are indebted to Professors L. F. Rettger and G. C. White for valuable suggestions in planning the work described herein.

SummaryAqueous solutions of penicillin (sodium salt) containing 5,000 Oxford Units per ml had slight irritating effects on the normal bovine mammary gland as measured by physical examination of the gland, body temperature and changes in the character and quantity of milk. The largest dose infused was 40 ml (200,000 O.U.). Increase in body temperature, tremors and greater changes in the character of the milk were observed after penicillin was introduced in large volumes of water. Largest volume infused was 950 ml (190,000 O. U.). These effects may have been due to the pyrogenic properties in the water used.In glands infused with small volumes of water containing 5,000 O. U. per ml., the rate of decline of penicillin per ml of milk is greatest during the first 10 hours after which the decline is at a slower rate. The milk contained 0.5 or more units of penicillin per ml 24 hours after the infusion of 30,000 or more units. The disappearance rate from pathologic glands was of the same order as for the normal ...