DR DAVY'S MISCELLANEOUS OBSERVATIONS ON THE BLOOD. 31 



and of 305 grs. of water. The fibrin was equal to 31 grs. After ten days its 

 volume seemed little diminished — 58*4 grs. of the clear fluid evaporated left -1 gr. 

 The undissolved residuary portion, constituting so large a proportion of the whole, 

 was soft, glutinous, and adhesive ; it might be called ropy, as it allowed of being 

 drawn out, and when agitated by a circular motion, it rose spirally in the liquid. 

 It thus differed from the dried fibrin, which was softened in a slight degree, but 

 not rendered glutinous. Examined after thirty-four days, it seemed little altered 

 in bulk, and nowise in its properties. The fluid was slightly viscid : a portion 

 of it, 41 - 4 grs., evaporated to dryness, yielded only 05 gr. It became slightly 

 turbid during evaporation at a temperature of about 180°, and when the ammonia 

 was driven off, it lost the little viscidity it before had. The smaller proportion 

 of residue in this instance might have been owing to the circumstance that the 

 phial holding the fibrin and the dilute aqua ammonise not being firmly corked, 

 some of the ammonia might have escaped. 



These results demonstrate how feeble is the solvent power of ammonia on 

 fibrin. Many other experiments which I have made, of which an account is 

 hardly needed, have been amply confirmatory of the fact, and also of the well- 

 known effect of ammonia in rendering fibrin viscid and glutinous, and of increas- 

 ing its transparency. This last effect should be kept in mind, otherwise, as the 

 refractive power of fibrin differs but little from that of water, it may in some 

 instances be imagined to be dissolved, when it is only diffused.* 



3. On the Serum of the Blood. — On this fluid the effect of ammonia is less 

 distinct. It appears to diminish rather than to increase the viscidity of the 

 serum, as is shown by the following experiment : a portion of the serum of the 

 blood of a pig, equal to 314 grs., was mixed with 274*4 grs. of aqua ammonias of 

 sp. gr. -89, in a glass-stoppered phial ; and about an equal quantity of the serum 

 of the same blood was poured into a similar phial. This was on the 30th March. 

 Each was shaken daily : froth was produced in each instance, but that from the 

 ammoniacal mixture subsided more rapidly than that from the serum alone ; and 

 the longer the trial was continued — it was continued more than a month— the 

 more marked was the difference. 



At the end of this time the ammoniacal mixture had deposited a white 



* When well-washed fibrin, still slightly coloured by the colouring matter of the blood, is placed 

 under the microscope, it appears to consist of translucent granules forming under gentle pressure a 

 connected tissue. On the addition of aqua ammonise it becomes clear and transparent, like jelly, 

 with a brightening of its colour. Compressed, it shows elasticity, and when extended by continued 

 pressure, so as to be very thin, its appearance is hyoloid ; no granules are to be seen in it except a 

 few scattered ones, which, it may be, were derived from blood corpuscles. 



Fibrin which has been rendered viscid by ammonia, after the removal of the ammonia by repeated 

 washing, gradually contracts, and from being transparent becomes, in consequence of condensation, 

 opaque, or nearly so. Thus contracted it often exhibits an imitative form, like that of hydatids. Its 

 retention of the colouring matter of the blood is remarkable ; it is greater even than that of the 

 capsule or walls of the corpuscles. 



VOL. XXIV. PART I. I 



