MILK. 155 



drops of the milk of the cow, the ass, or the goat, which pass 

 through the filter, and which are generally white and opaque, 

 being rejected, and the second portion of filtered milk being 

 preserved and allowed to remain undisturbed for a few 

 minutes, it will be seen to separate into two parts, the in- 

 ferior of which is clear and transparent, while the superior is 

 somewhat opaque ; now if a drop of the fluid of this inferior 

 layer be examined with the microscope, it will be found to 

 contain an innumerable quantity of globules of exceeding 

 minuteness and refracting the light but feebly, as well as 

 occasionally other globules more rare, larger, and refracting 

 the light very strongly ; the former are the cheese globules, 

 and the latter the proper milk globules. 



THE GLOBULES. 



It is to the presence of the globules which occur in such 

 vast quantities in each drop of healthy milk that the colour 

 and opacity of that fluid is due.* 



These globules are of perfect rotundity, their surface being 

 smooth, presenting a pearly aspect, and refracting the light 

 strongly ; the circumference of each globule is dark and the 

 centre light : the globules vary greatly in size ; the smallest, 

 which are in active molecular movement, being reduced to 

 mere points and not exceeding the y^uo^ ^ an m ch, the 

 largest frequently attaining the sVoo f an inch, and the 

 medium size ranging between the ^Vo" ^ an ^ ncn m ^ia- 

 meter and the ^ l ^. (See Plate XIV. fig. 1.) In milk 

 which is healthy the globules float freely in the serum, and 

 do not adhere to each other. 



Such is the form, appearance, and variety of size exhibited 

 by the milk globule ; much difference of opinion has existed 



* Leeuwenhoek first clearly indicated the existence of these globules 

 in the milk in the following terms : " Vidi multos globulos, similes sextae 

 parti globuli sanguine! ; et etiam alios, quorum bini terni aut quaterni se 

 invicem modo attingebant, fundum versus descendere ; et multos varise 

 magnitudinis globulos in superficie fluitantes, inter quos posteriores adipem 

 sive butyrum esse judicabam." 



o 2 



