Compounds, such as sugar, in the blood of wood frogs protect them from freezing temperatures by affecting how water freezes in the body.

References

“The accumulation of high levels of low-molecular-weight solutes (polyhydric alcohols, saccharides [e.g., the sugar glucose]) provides cryoprotection to freeze-tolerant animals by minimizing, via colligative [binding] effects, the percentage of body water converted to extracellular ice and the extent of cell volume reduction…[F]reeze-tolerant frogs respond to ice formation in peripheral tissues by synthesizing large amounts of glucose in the liver and rapidly distributing the sugar throughout the body…Proton magnetic resonance imaging of freezing and thawing in whole frogs showed a new adaptive effect of the very high glucose levels in core organs; during thawing, organs such as liver and heart melted first, allowing recovery of their vital functions to begin while the rest of the frog thawed.” (Storey 1997:319)

Journal article
Organic Solutes in Freezing ToleranceComparative Biochemistry and Physiology Part A: PhysiologyJuly 1, 1997
Storey KB

“Seminal studies of freeze tolerance in woodland frogs have documented their efficacious system for copiously mobilizing glucose or glycerol in direct response to corporal freezing (Schmid, 1982; Storey and Storey, 1988). Cryoprotectant is chiefly derived from glycogen that accumulates in liver, representing up to 20% of organ mass, during late summer and autumn. Triggered by ice nucleation, its synthesis and export to other tissues proceeds rapidly, with concentrations in blood and core organs ultimately reaching 100–250 mmol l−1. Such levels are readily tolerated by these frogs, but would be deleterious in endotherms. Upon thawing, cryoprotectant is returned to the liver and reconverted to glycogen; reabsorption of glucose in the urinary bladder assists this process and limits the excretory loss of this valuable solute (Costanzo et al., 1997a).” (Costanzo and Lee 2013:1965)

Journal article
Avoidance and tolerance of freezing in ectothermic vertebratesJournal of Experimental BiologyMay 15, 2013
Costanzo JP; Lee RE, Jr.

Journal article
Wood frog adaptations to overwintering in Alaska: new limits to freezing toleranceJournal of Experimental BiologyApril 15, 2014
Larson DJ; Middle L; Vu H; Zhang W; Serianni AS; Duman J; Barnes BM

Journal article
Natural freezing survival in animalsAnnual Review of Ecology and SystematicsNovember 1, 1996
Storey KB; Storey JM

Web page
Cryoprotectant Molecules - Nature's Anti-freezeSeptember 18, 2011
The Naked Scientists.

Living System/s

Organism
Wood FrogLithobates sylvaticusSpecies