298 



Bulletin 1Y8. 



There will be seen in figure 58 a slight constriction indicating the 

 boundary between the duct of the teat and tlie milk cistern proper. 

 In tlie examination of the udders incident to the bacteriologic work 

 care was taken to ascertain if there was present a distinct barrier 



separating the milk cistern 

 from that of the teat. Such 

 was not found. There was 

 seen, however, a considerable 

 variation in the size of the con- 

 striction in the different quar- 

 ters of the several udders. 

 The presence of circularly dis- 

 posed plain muscle fibres in 

 the constriction of the mucous 

 membranes and in the mucosa 

 throughout the whole length 

 of the teat has been demon, 

 strated by the writer by liisto- 

 logic methods. The point to 

 be emphasized is that no ob- 

 struction capable of excluding 

 bacteria from the milk cistern 

 exists, except, perhape, the 

 sphincter muscle at the lower 

 end of the teat.* 



Plate 1 shows much better 

 the system of milk channels in the udder. One-half of the udder 

 of a cow was injected through the teats with a mass of hot gelatin 

 containing lampblack in suspension. After cooling, which solidi- 

 fied the gelatin, a section was made and photographed. The gela- 

 tin was previously removed from the cavities of the teat, milk 



Fig. 58. — A plaster of Paris cast of the 

 interior of the teat and milk cistern 

 of one quarter of an udder. 



* Dr. R. G. Freeman has observed that the milk of some cows when drawn 

 from the udder with aseptic precautions shows a considerable bacterial content 

 even aftdr the milking period is more than half completed. He has also found 

 that this invasion is much more marked in the udders in which the ends of the 

 teats are imperfectly closed by weak sphincter muscles than in those possessing 

 teats which are firmly closed at their lower extremities. — From unpublished data 

 furnished by courtesy of Dr. Freeman. 



