DR DAVY'S MISCELLANEOUS OBSERVATIONS ON THE BLOOD. 27 



observed from incipient thaw. During the whole time, as denoted by the test 

 employed, ammonia was evolved, and, as well as I could judge, the lower the 

 temperature the larger was the quantity. I need hardly remark that there was no 

 appreciable contraction of the crassamentum, no further separation of serum after 

 congelation had taken place. The serum which first exuded before congela- 

 tion—a very small quantity— after having been frozen, became coloured, and, 

 finally, of a red nearly as dark as the general mass, and this owing in part 

 to blood corpuscles suspended in it of altered form, and in part to solution of 

 their colouring matter. After thawing, the blood had no smell indicating pu- 

 tridity, nor did it discolour silver ; yet it continued, at a temperature of 50°, to 

 evolve ammonia, and much in the same proportion as when frozen. Now, how- 

 ever, the contraction of the crassamentum, i.e., of its fibrin, before arrested, took 

 place, and to an extent seemingly differing but little from what would have 

 occurred had the blood not been frozen. The blood corpuscles now were so 

 reduced in size, and had become so transparent, that unless dried, they were seen 

 with difficulty, and not without the most accurate adjustment. 



These results, viz., the disengagement of ammonia, and, we must infer, its 

 formation, when blood is frozen, are hardly such as could be expected ; and they 

 are the more remarkable, as seeming to be independent of putrefaction and the 

 action of oxygen, and owing to a new arrangement of elementary parts produced 

 by a low temperature, one ranging from about 50° to many degrees below the 

 freezing point. That congelation was not essential to the formation of the 

 ammonia was shown in other experiments, in which, when blood was exposed to 

 a temperature ranging in one trial from 32° to 34°, the volatile alkali was pro- 

 duced, and in others at a temperature varying from 40° to 50° ; and, in the latter, 

 even when continued several days, without any indications of putridity, judging 

 from the absence of the smell such as denotes putrefaction, and from silver 

 immersed remaining untarnished. 



At first view what has been described may seem anomalous, yet the results 

 are not without analogies. The potato, as is well known, becomes sweet from 

 the conversion of starch into sugar by " frosting ;" and the ripening of the grape, 

 the sweetening of its juice, it is also well known, is hastened by the setting in of 

 frost at the time of the vintage in Switzerland, and in other countries with a 

 similar climate. The formation of peat is another example of the efficiency of a 

 comparatively low temperature in producing new compounds. Familiar with the 

 effects of heat — i.e., of a high temperature— as an active agent, it is not perhaps 

 surprising that cold — i.e., a low temperature — should be little thought of except 

 as the opposite and the antagonist of heat, disregarding the fact that they differ 

 merely in degree; and how inconsiderable that is, whether measured by our 

 sensations or by the thermometer. 



After witnessing the effects of congelation on blood, the question occurred, Is 



VOL. XXIV. PART I. H 



