354 



SCIENCE- GOSSIP. 



possible glycerides. Thus the fat may consist of 

 tri-glycerides such as : — 



< Stearic A. 

 Stearic A. 

 Stearic A. 



/Palmitic A. /Oleic A. 



G.e-Palmitic A. G.e— Oleic A. 



\Palmitic A. \01eic A. 



These compounds have been artificially prepared, 

 and are known as stearin, palmitin, and olein. 



Or there may be a series of mixed glycerides 

 such as : — 



< Stearic A. 

 Stearic A. 

 Palmitic A. 



< Stearic A. 

 Palmitic A. 

 01°ic A. 



< Palmitic A. 

 Oleic A. 

 Line-lie A. 



There is evidence that in some cases, at all events, 

 such mixed glycerides do exist. 



When we examine the mixed fatty acids obtained 

 from any fat we are met by an initial difficulty. 

 There is no exact method of separating the solid 

 acids from the liquid or unsaturated acids, and we 

 have in most cases to be content with drawing 

 inferences from the percentage of iodine absorbed, 

 by the mixture, or its incompletely separated frac- 

 tions. In the case of stearic acid, however, Mr. 

 Hehner and the present writer have devised the 

 following means of effecting a quantitative sepa- 

 ration. Strong alcohol is saturated with pure 

 stearic acid, and the flask containing the solution 

 left all night in a mixture of ice and water, the 

 clear liquid being filtered off next morning from 

 any deposit. On treating the mixed fatty acids 

 with this saturated solvent, and cooling the flask 

 overnight in ice-water, the alcohol, having already 

 been saturated with pure stearic acid, is unable to 

 dissolve any more, although it can take up all the 

 other constituents. 



The liquid is filtered off by means of the appa- 

 ratus shown in fig. 5, and the deposit in the small 

 flask weighed. The filter is the thistle-funnel, 

 the mouth of which is covered with linen and 

 immersed in the flask, and a suction pump is 

 attached to the indiarubber tube fixed to the side 

 tubulure of the large flask. 



By this method light has been thrown on many 

 obscure points, as, for instance, the nature of 

 fat crystals. If we dissolve a fat in ether and 

 allow it to crystallise, characteristic microscopic 

 crystals are frequently obtained. Thus lard yields 

 straight crystals with chisel-shaped ends, whilst if 

 beef-fat be taken, the crystals have the form 

 shown in fig. 2. A mixture of lard with about 

 fifteen per cent, of beef-fat gives crystals of inter- 

 mediate character (fig. 1), the grouping resembling 

 those of fig. 2, and the chisel-shaped ends those of 

 ordinary lard. 



In certain cases lard from the flare of the pig 

 yields crystals closely resembling those in fig. 1, 

 and the explanation of this was found in the 

 following experiment : A lard containing sixteen 

 per cent, of stearic acid was dissolved in ether, 

 and yielded an abundant deposit of crystals with 

 the characteristic chisel-shaped ends, which were 



found to contain thirty-two per cent of stearic acid. 

 This deposit was again crystallised from ether. 

 The crystals were then needle-shaped, but had 

 distinct chisel-shaped ends, as in fig. 1. They 

 contained forty-seven per cent, of stearic acid. 

 For a third time the deposit was recrystaliised. 

 The percentage of stearic acid had now risen to 

 fifty-nine per cent., and the crystals were hardly 

 distinguishable in form from those of beef-fat 

 (fig- 2). 



It thus appears that the difference in form 

 between the two kinds of crystals is solely due to 

 a larger proportion of stearic acid, and that in 

 exceptional cases the fat from certain parts of the 

 pig contains more of that acid, and thus yields 

 pointed crystals in one crystallisation. 



Experiments were next made with fat from 

 different parts of the same pig, and the following 

 amounts of stearic acid were found : head, 9 ; ham, 

 9 ; breast, 11 ; flare, 15 : and back, 9 per cent. 



In a similar series of determinations with sheep- 

 fat the results were : back, 25 ; neck, 16 - 4 ; breast, 

 1 ; ham, none ; and kidney, 27 per cent, of stearic 

 acid. The ham fat. which contained no stearic 



FAT CELLS. 



Pig. 3. Fat-cells from Rabbit. 



acid, was liquid at the ordinary temperature, and 

 that of the breast nearly liquid. 



A specimen of beef-fat, which was very hard, 

 was found to contain fifty per cent, of stearic acid. 



These results show that there is a relation 

 between the consistency of the fat and the pro- 

 portion of stearic acid. 



Some interesting observations on the variations 

 in the consistency of the fat from different parts 

 of several animals have recently been made by 

 Henriques and Hansen. They have found that the 

 fat gradually varies in composition from the 

 exterior to the interior parts of the body. The 

 fat immediately below the skin has the lowest 

 melting-point, and that in the centre of the body 

 the highest, whilst the melting-point of the fat in 

 the intermediate parts varies with its distance 

 from the interior. 



