222 SPECIFIC GRAVITY OF CREAM. 



EXPERIMENT IX. 



A microscopic investigation would seem to settle 

 the question that some cream may be lighter, other 

 cream heavier than water. 1 added some miik to 

 water in a tall glass tube. The milk all fell rapidly 

 to the bottom, in a smoky cloud, leaving the upper 

 third of the tube absolutely clear. In half an hour 

 the density at the bottom had diffused itself upwards, 

 in a regular gradation of opacity, even to the top. 

 Upon examining a drop from the surface of the water, 

 under the microscope, globules showed of quite even 

 sizes, ranging generally from 6750" to 4500" in diam- 

 eter. A like examination of the bottom layer scarcely 

 showed a globule larger than 9000" in diameter, yet 

 two globules were seen as large as 6750". 



Having now considered the formation of milk in 

 respect to one of its constituents, and treated the 

 subject in a general manner, we are now prepared to 

 examine into the peculiarities which come of breed 

 and are consequent thereto. 



My opportunities have been limited to three breeds, 

 the Ayrshire, the Jersey, and the Dutch, those 

 large black and white cattle from Holland, the Amer- 

 ican "Holsteins." Although such differences as are 

 to be discussed are probably of universal application, 

 yet here my conclusions will be confined to the result 

 of my own examinations, which have been fairly 

 complete with reference to the Ayrshire and Jersey 

 milks, but more limited with the Dutch. 



