NO. 1879. PRESERVATION OF OSS EOUS TISSUES— BOETTCHER. 701 



traiy, the more a fluid approaches a colloidal condition the less it 

 will penetrate. 



Paraffin is not a perfect material for the preservation of objects, 

 but it approaches perfection more nearly than any other substance 

 known. It has the fault, however, of contracting upon coolmg, and 

 this contraction amounts to 14 per cent. Wlienever an object has 

 absorbed to saturation a fluid at 100° C, each capillary, at ordmary 

 temperatures, will contam only 86 per cent of solid paraffin, crystal- 

 lized, and 14 per cent interstitial spaces. These spaces may con- 

 taui, besides the lower members of the series, also impurities, air, or 

 even oxygen, according to Lippmann and Hawliczek, which has pene- 

 trated successively mward as contraction takes place, gradually fol- 

 lowing the coolmg process. It is to be observed, however, that in a 

 capillary or larger vessel the wall, rather than the mtercellular 

 lumen, attracts the layer. The slide test will prove this. Paraffin 

 allowed to cool between a clean, dry slide and a cover glass will 

 show a matted mass of fatty crystals arismg from, or adhermg to, 

 a thin layer of the same on each glass. 



Air, then, will filter through and approach the material which is 

 to be protected, but does not reach it. These crystals act as a filter, 

 like the cotton wad in a culture tube, only more thoroughly and on a 

 more extended scale. 



There is one danger, however, that is greater than the preceding. 

 When by progressive inward cooling an inhalation of air takes place, 

 impurities such as spores of fungi and bacteria may also penetrate 

 one or two layers of crystals, and thus become embedded in the 

 surface of the paraffin. These, if conditions are favorable, may 

 attract moisture from the atmosphere, and accordmg to Dr. O. 

 Rahn,- grow and decompose the paraffin. If, as the above authority 

 claims, paraffins of -a lower melting point form better media for such 

 growth than those of a higher meltmg pomt, the reason may be 

 found m the more porous condition of the external layers owing to 

 the greater evaporation of the lower series occurrmg as impurities 

 in the grades of paraffins used. The growth of species of Penicillium 

 and Aspergillus on the paraffin of fruit jars can be easily explained 

 by the fact that the porosity of the crystallized paraffins, as well as 

 the expension and contraction of the preserved material closely 

 below the paraffin, even if the latter does not become detached from 

 the sides of the jar by this movement, causes an alternate pressure 

 of liquid outward or a suction of spore-laden air mward, and the 

 conditions for a growth of fungus are perfect, provided the layer 

 of paraffin is not too thick. If it be too thick no mold will form, 

 but the air will enter and cause a more or less advanced state of 

 vinous fermentation. 



1 Centralbl. Bakt., Abth. 2, Jena. 1906, vol. 16, p. 382. 



