26 DR DAVY'S MISCELLANEOUS OBSERVATIONS ON THE BLOOD. 



what varied ; it seemed greatest in those of the common fowl, least in those of 

 the ox. 



IV. On the Effect of a Loiv Temperature on the Blood. 



It was ascertained by Hewson that the blood, by rapid freezing, is not de- 

 prived of its property of coagulating when thawed ;* besides this and the change 

 of form of the corpuscles from refrigeration which I have observed,! I am n °t aware 

 that any thing has hitherto been published respecting the agency of a low tem- 

 perature on this fluid. 



During the frost which prevailed in the Lake District the winter before last, 

 from the 2d to the 10th of January, I had an opportunity of renewing the inquiry. 

 The blood used was that of the turkey, of the common fowl, and of the sheep. The 

 most remarkable result obtained was that a low temperature, like a high tempe- 

 rature, appears to promote not only a change of form of the red corpuscles, but 

 also a change of composition, as indicated by the production of ammonia and the 

 solution in the serum of the colouring matter of the blood. As the changes were 

 the same whichever blood was the subject of experiment, I shall restrict myself 

 to what was observed in the trials on that of the common fowl. On the 4th of 

 January a wine-glass was nearly filled with the blood of a full-grown fowl as it 

 flowed from the divided great cervical vessels; it coagulated in less than two 

 minutes. A plate of glass, moistened with a drop of dilute hydrochloric acid, 

 was placed over it. After ten minutes there was a copious deposition of dew r on 

 its inner surface, vapour from the warm blood beneath, and there condensed. On 

 examination w r ith microscope, after evaporation, not a trace of muriate of am- 

 monia could be detected. The trial was repeated, and for six hours in the open 

 air, at the temperature of 28° Fahr. ; now a trace barely of the salt was found 

 The blood was moderately florid, preserving its original appearance, and was not 

 yet frozen. It was left out during the night. The temperature during the time, as 

 shown by a register thermometer, was as low as 12° ; on the following morning, 

 at a.m., it had risen to 18°. The blood was found to be frozen hard and 

 thoroughly ; it was greatly darkened in colour, and had lost entirely its florid 

 hue. Distinct crystals of muriate of ammonia, and these not a few, were detected 

 on the covering glass after the evaporation of the acid, and the red corpuscles 

 from elliptical had become circular and globular. 



The observations were continued until the morning of the 10th, when a thaw 

 set in. The blood was examined twice daily, viz., at 9 a.m. and at 3 p.m. During 

 the period the temperature was always below 20°, but not lower than 15°, excepting 

 once, as already mentioned. The day temperature ranged as high as 27°, it was 

 never lower than 22°. At the former temperature, a softening of the blood was 



* Hewson's "Works, p. 25. 



f Physiological Researches, p. 369. 



