DIRTY MILK 71 



This is due largely to the fact that while the visible particles 

 are held back, the lumps of manure, dirt, and bacterial 

 clusters are broken up. Therefore, when the bacteria are 

 counted we obtain a thousand or more colonies where only 

 one developed before. 



The initial contamination of milk. For the most part, 

 bacteria do not pass a healthy udder. However, we can 

 place no trust in the filtering ability of the mammary 

 gland. It is known that the virus of foot-and-mouth dis- 

 ease, which is so tiny as to be ultramicroscopic, and the 

 virus of milk sickness, and the micrococcus causing malta 

 fever are found in the milk of affected animals; that is, the 

 milk of such animals contains the virus even though the 

 udder may not be diseased. There is good evidence that 

 the tubercle bacillus does not appear in the milk as it leaves 

 the teat, unless there is tuberculosis of the udder, and the 

 same is true of most of the pathogenic micro-organisms, 

 with the exceptions above noted. 



We know that milk freshly drawn from the udder under 

 ordinary circumstances practically always contains some 

 bacteria. Thus I have found that milk obtained by careful 

 methods from separate cows had from 60 to 8300 bacteria 

 per cubic centimetre. These numbers evidently do not 

 represent the real number of bacteria present, for the rea- 

 son that not all the bacteria produce visible colonies upon 

 agar plates, and further, each colony does not necessarily 

 represent the growth from one micro-organism. The bac- 

 teria in fresh milk are very apt to agglutinate into clusters. 

 This milk which contained from 60 to 8300 bacteria per 

 cubic centimetre was obtained by first washing and disinfect- 

 ing both the udder and the hands of the milker as though 

 preparing for a surgical operation. A sheet wet with bi- 

 chloride of mercury was then placed around the cow, leav- 

 ing only the teats projecting through appropriate openings. 

 The fore milk was discarded and the samples to be exam- 

 ined were drawn immediately into sterile test tubes. De- 



