358 



MILK. 



distinguished would be ^th or ^th of 

 a line square, and thus they would be much 

 larger than those of whose existence a very 

 simple process of reasoning is sufficient to con- 

 vince us. 



BIBLIOGRAPHY. The following works may be 

 referred to. Hoohe, Micrographia, Lond. 1665. 

 Baker, Of Microscopes, Lond. 1785 Adams, On 

 the Microscope, Lond. 1787. Brewster, Treatise 

 on the Microscope from Encyclopaedia Britannica, 

 also Treatise on new Philosophical Instruments. 

 On Optics, Lanlner's Cyclopaedia. Lister, in Phil, 

 Trans. 1829. Chevalier, Des Microscopes, Par. 

 1839. Mandt, Traite Pratique du Microscope, Par. 

 1839. Pritchard and Goring, Micrographia ; also, 

 by the same authors, Microscopic Illustrations and 

 Microscopic Cabinet. Slack, Holland, and Turrell, 

 in Trans. Soc. Arts, vol. 49. Penny Cyclop, art. 

 Microscope. Hildebrandt, Anatomic, Band. i. p. 128. 



( W. B. Carpenter.) 



MILK. (rX, Gr.; lac, Lat.; le lait, 

 Fr.; die Milch, Germ.; latte. Ital.) The 

 secretion of the mammary gland. In treating 

 of the milk it will perhaps be best, previous to 

 entering upon its description as produced by 

 the human subject, to give a general account 

 of the secretion as obtained from the cow, such 

 being the most familiar example afforded to us. 

 Milk may be regarded as a serous fluid, hold- 

 ing in suspension minute white globules com- 

 posed of casein and fatty matter. These glo- 

 bules have been microscopically examined by 

 Raspail, who states them to have a diameter 

 of .00039 inch, and to disappear on the 

 addition of a solution of potassa. The most 

 recent microscopic observations on the milk are 

 those of Professor Nasse, of Marburg,* who 

 gives the following as the constituents of the 

 normal secretion of the mammary gland: 1st, 

 smooth, homogeneous, transparent oil globules 

 and large oil globules, also the common milk 

 globules; 2d, cream globules, distinguishable 

 by their facette-like appearance; 3d, granu- 

 lated yellow corpuscles; 4th, the lamellae of 

 epithelium ; 5th, the more or less turbid 

 medium in which the four preceding kinds of 

 corpuscles are suspended. 



The common milk globules are composed of 

 fatty matter, which dissolves rapidly in ether. 

 No membrane can be seen investing them. The 

 first nine days after delivery the largest globules 

 measure 3jj th of a line in diameter, but subse- 

 quently become as large as -r^th, but they vary 

 in size throughout lactation. The cream glo- 

 bules are considered by Professor Nasse to be 

 formed after the milk has been drawn or 

 exposed to the air, for in fresh woman's milk 

 no globules but the common milk globules 

 above described are discernible : the cream 

 globules occur as large as J th of a line in dia- 

 meter. The yellow granulated corpuscles are 

 peculiar to the colostrum ; their diameter is 

 from -f^th to ^tli of a line ; some are found mea- 

 suring 3 ' g th of a line in length and ^th in breadth. 

 They are composed of fatty matter. The author 

 considers them analogous to the mucus cells 

 cast off from mucous membranes, and thinks 

 that perhaps they come from the gland ducts. 

 From my own observations I am inclined to 



* Mullcr's Archiv, 1840, Heft iii. p. 258. 



think that the cream globule of Nasse exists 

 even in fresh milk, and may easily be seen in 

 specimens containing but little fatty matter. I 

 lately saw them in the milk of a woman who 

 had suckled for seven months. I have not 

 been able to rid the milk of globules by ether 

 or liq. potassa:. If milk be agitated with ether, 

 then allowed to stand, and the lower stratum 

 of fluid examined, we can detect distinct 

 globules in it globules of all sizes, and having 

 the appearance described by Nasse as belonging 

 to the cream globule. From the variety in size 

 which I have so constantly observed, I cannot 

 understand how any author can have made up 

 his mind to give an admeasurement to the 

 globule of milk ; for my own part, after much 

 careful observation, I feel convinced that the 

 milk contains nothing which deserves the name 

 of a true organic globule. That globules exist 

 I do not deny, and these I believe to be what 

 have been described by Nasse as cream glo- 

 bules, appearing when milk has creamed, be- 

 cause the adhering fatty matter is separated ; 

 but, notwithstanding, being very obvious before 

 creaming occurs, in specimens of fresh milk 

 containing a small proportion of fatty matter. 

 The serum in which these particles float is 

 composed of water, holding in solution an 

 alkaline lactate and chloride with traces of 

 sulphate and phosphate, lactates of lime and 

 magnesia, sugar of milk, and animal extractive. 

 Oxide of iron and an earthy phosphate are to 

 be detected in the ashes of milk, but these, in 

 all probability, are derived from the casein of 

 the secretion. When milk is allowed to remain 

 at rest for some hours, a pellicle forms on its 

 surface, varying with the nature of the milk : 

 this is what is called the cream, and consists of 

 the fatty or butyraceous matter of the milk in 

 combination with a varying proportion of casein. 

 It is from this cream that butter is obtained by 

 churning, by which operation the butyraceous 

 particles unite into a mass to the exclusion of 

 the casein, which remains suspended in the 

 serum, and thus forms a mixture known by the 

 name of butter-milk or lait de beurre of the 

 French. The whole of the casein, however, 

 cannot be removed from the butter by churning, 

 its minute particles being entangled by the 

 cohering fatty globules, and it is in a great 

 measure owing to its presence that butter is 

 more or less prone to become rancid and de- 

 composed. Milk from which the cream has 

 been removed still retains the greater part of 

 the casein, and when this is precipitated from 

 it by the action of rennet, we obtain a curd, 

 which, being pressed and dried, constitutes 

 cheese. The clear liquor separated from this 

 curd contains the more soluble matters of milk, 

 viz. the alkaline salts with the sugar of milk, 

 and in Switzerland a considerable quantity of 

 this sugar is manufactured from whey and used 

 for household purposes. I have thought it 

 best to notice the various operations in domestic 

 economy to which the milk is subjected, not 

 only because by them several of its proximate 

 elements are eliminated, but likewise that the 

 reader may have some familiar object with 

 which to connect the following account of the 



