^8 MetHoir on the Nature of Jul Suhstancci, 



ance of the microscope, in the fats which are not too soft* 

 However this may be, tiie fatty substance, hquid or soHd, fixed 

 or volatile, and wherever we meet with it in orgatiizcil beings, 

 presents nearly the same structure in the reservoir where nature 

 has placed it. — To give some examples of this taken frcni the 

 vegetable kingdom, I shall cite among the plants which secrete 

 the sehaceo-cirous matter, the corpuscles which constitute the 

 dust of the leaves and fruits which Proust has found analogous 

 to wan. On examining this dust with the microscope, we see it 

 formed of transparent grains, the form of which varies v, ith the 

 species: an analogous configuration may be remarked in the 

 waxy substance which coats the surface of myrtle-berries. It 

 is sufficient to press strongly the latter, in order to free them 

 of the wax, which has a grainy and amylaceous appearance. 

 The volatile oils are also contained in small membranous blad- 

 ders, as is proved by the epithets of vesicular, niiliarv, globu- 

 lous glands, which botanists have given to these small reservoirs 

 filled with volatile oil. I shall not inquire, with physiologists, if 

 the secretion of the suet or of the fat operates, as ihey pretend, 

 by the extremities of the arteries, or by oozing through their 

 tunics: one thing is certain, that this secretion takes place un- 

 der certain circumstances with incredible celerity. 



Suet does not exist in a state of absolute purity in animals, 

 and hitherto it has been unknown any where in that state: the 

 firmest which can be procured still contains a certain quantity 

 of oil; that which incloses the kidneys in sheep contains more 

 than that of bullocks: the tallow used for candles also furnishes 

 a great quantity; for 100 parts at the temperature of 5" R. yielded 

 30 parts of oil. We succeed in depriving these fatty substances 

 of their oil by melting them and adding spirit of turpentine 

 newly distilled ; the mixture, frozen and pressed in a cloth, or 

 what is still better in gray paper, leaves the suet in a state of 

 purity: it is only necessary to keep it in fusion for some time, 

 and allow it to cool. Pure mutton suet thus obtained is a sub- 

 stance very analogous to wax, and seems even to be more com- 

 pact, drier, and more brittle; but it has not the same ductility, 

 for it is easily reduced to powder ; it likewise waxes bodies, giving 

 them a glossy appearance like bees-wax, and emitting the same 

 noise on being rubbed*. Pure mutton i&uet melts at the tem- 

 perature of 49° R : yellow wax melts precisely at the same de- 



* Fatty substances as well as ccrtnin families of organized beings seera 

 to contain a great qnantity of :^pccies vliicli pass to each other liy siiaiies 

 so sHulit that it is diHicuJt to group tlicm well: tluis we are freqiienlly 

 embarrassed, when it is wanted to rai.ue this or that iatly substance, 

 vvhetlier lo do so among the waxes, the suets, or the adipocires, and it must 

 be adiniiLcd llial the lust three genera are purely artificial. 



grce 



