SECT. 6.] MILK- AND FAT- GLOBULES. II 



them arc physiologically related to the elementary granules in so 

 far as that when once formed they do not enlarge, and as they 

 multiply neither by divisions nor by endogenous formations. The 

 milk-globules which, as Henle first asserted, consist of the fats 

 of the milk, and of an envelope of caseine, may with tolerable 

 certainty be arranged under this division. The immeasurably 

 small molecules, also, of the chyle and blood, are, according to 

 //. Muller's investigation, fat globules with a proteine envelope, and 

 similar vesicles may also occur in most other fatty and albuminous 

 fluids. That is to say, since the discovery of Ascherson (Muller's 

 ArcJdv. 1840, p. 49), that whenever fluid fat and fluid albumen are 

 shaken together, all the fat-drops formed become surrounded with 

 a delicate envelope of albumen, it is more than probable that 

 wherever in the body fat and albumen come in contact in a fluid 

 condition, similar vesicles are formed. 



The elements occurring in the yelk of certain animals form a 

 peculiar group of elementary vesicles. They are best known 

 in the yelk of the fowl, in which the globules of the proper 

 yelk-substance and of the vitelline cavity, are, as Schwann dis- 

 covered, all vesicles, although they have not the importance of cells. 

 The membranes of these yelk-vesicles are exceedingly delicate, and 

 consist of a proteine compound ; the contents are fluid albumen in 

 which, in the globules of the vitelline cavity, there usually lies a 

 large parietal, in the others, numerous larger and smaller fat-drops. 

 The development of these vesicles probably proceeds from the fat- 

 drops, as in other elementary vesicles, from which, however, they 

 are distinguished by their possessing a very distinct growth, and 

 undergoing metamorphoses in their contents, seeing that, in many, 

 the number of the fat-drops increases more and more with age. 

 Similar vesicles can also be demonstrated in the yelk of fishes, 

 crustaceous animals and spiders, and, as in birds, have only a 

 transitory importance, inasmuch as they are not employed directly 

 in the formation of the body of the embryo, but only serve as 

 nourishment for it. Lastly, free nuclei are met with in some places, 

 as in the wall of the vesicles of the thymus, and in the rust- 

 coloured lamina of the cerebellum. 



With regard to the mode of the formation of " Ascherson's vesicles," as they 

 are called, Witticli has quite recently furnished some information. According 

 to Wit/icJi, whenever oil and albumen come in contact, a part of the fat is 

 inified by the alkali combined with the albumen ; by these means, the 

 layer of albumen lying next to the oil (because poorer in alkali), is rendered 

 insoluble, and precipitated as Aschersoti's ''Haptogen Membrane," as it is called. 



