1902-3.] Bacterial Contamination of Milk. 477 



Another marked characteristic of all the species was that they were 

 facultative anaerobes. The anaerobic faculty was especially marked in 

 the two species, Nos. i and 2, that were found to be so uniformly 

 present in all the milk tested. This is just what one would naturally 

 expect, for the conditions in the udder must be largely anaerobic 

 conditions. In virtue of these conditions, and possibly other undeter- 

 mined conditions, the udder, so to speak, exerts a selective action upon 

 the bacteria which may be temporarily present in it. In this they are, 

 of course, aided by the mechanical expulsion of bacteria in the process 

 of milking. 



In order to throw a little light upon this problem, experiments 

 were conducted in inoculating udders with well-marked but harmless 

 bacteria, which could be easily recognized by their cultural characteris- 

 tics. Bacillus prodigiosus and B. exiguum, both of which were marked 

 by their pigment production, were the ones experimented with. Cul- 

 tures of these were smeared upon the ends of the teats, so that the 

 bacteria might work their way up into the udder, just as any other germ 

 might which comes in contact with the ducts of the teat. In the case 

 of B. prodigiosus, about 20,000 per c.c. were present in the fore-milk at 

 the first milking eight hours after inoculation. By the third milking 

 only a few were present, and after that it disappeared completely. The 

 experiment was repeated with B. exiguuni with similar results, although 

 a smaller number — 240 per c.c. — were present in the first milking, and 

 by the fourth milking it had disappeared. No doubt the small number 

 was due to the fact that this germ grows more slowly than B. pro- 

 digiosus. 



In view of Ward's discovery of B. fluorescens liquefaciens in the 

 udders of certain cows, it seemed advisable to attempt to colonize this 

 germ in the udder, and a bouillon culture was smeared upon the ends of 

 the teats of a cow in the manner already described. This bacillus was 

 discovered in the fore-milk six hours after the teats were smeared, but 

 was not found in the fore-milk of the second and third milkings. 



It does not seem probable that an aerobic bacterium of this 

 character is able to live and compete with facultative anaerobic bacilli. 

 Further, the optimum temperature for the fluorescing bacterium is not 

 37°. 



Possibly, by continuous experimentation, we might have finally dis- 

 covered a species which would persist in the udder, but at the same 

 time, the bacteria chosen have evidently fared much the same as other 



