dr davy's miscellaneous observations on the blood. 21 



smaller is the quantity of water that is required to alter their form. As to their 

 hygroscopic property, this is shown by the simple experiment of breathing on 

 them, or by exposing them over water for a few hours, keeping them, of course, 

 out of contact with the water. In the instance of the warm vapour of the breath, 

 one expiration is sufficient to deprive them, previously dried, of their elliptical 

 form. 



It is worthy of remark, that when the corpuscles are coloured by the addition 

 of a weak solution of iodine, not only the action of the warm vapour of the 

 breath is in a great degree arrested, but even the action of water, and this after 

 immersion in water on a glass support for twelve hours, when they were found to 

 retain their normal form, only slightly contracted, with their nuclei distinct. May 

 it not be conjectured from this, that iodine medicinally used may operate in a 

 degree similarly, and thus may arrest undue metamorphic disintegration ? 



II. On the Changes xohich take place in the Blood when excluded from the Air. 

 The changes to which the blood is subject when exposed to the air, at ordi- 

 nary atmospheric temperatures, are pretty well known. To endeavour to ascer- 

 tain what would happen were air as much as possible excluded, the following 

 experiments were made : — 



A bottle full of water, deprived of air by the air-pump, was emptied the 

 instant before receiving blood from the divided cervical vessels of a barn-door 

 fowl ; so soon as full to overflowing, it was closed with a glass stopper lubricated 

 with oil, and inverted in water. 



During the first hour the blood retained its original hue, bright vermilion, and 

 this throughout. After two hours the colour had lost something of its brio-ht- 

 ness. The following day the colour had become uniformly chocolate brown. 

 The day after there was no appreciable change. The serum which had separated 

 was of a wine yellow, and the crassamentum had contracted considerably. On 

 the third day the serum was beginning to show a reddish tinge. From this day, 

 viz., the 9th of November, to the 4th of December, the serum became of a darker 

 red, and, like the crassamentum, was almost black, as seen by reflected light. 

 During the time mentioned, the temperature of the room in which the blood was 

 kept varied from about 55° to 58°. The bottle was now taken out of the water, 

 which was as clear as at first, showing that the closure was complete. The 

 stopper was drawn out with ease, proving— as it was introduced when the blood 

 was warm — that there was pressure from within rather than from without, 

 though there was no appearance of any gas evolved. The serum decanted was 

 of a dark purplish-red, as seen in thin layers by transmitted light, but black by 

 the same light, and opaque, in a tube of one-half inch diameter. The crassamen- 

 tum, of the same colour, was soft and easily broken up, and had, as well as the 

 serum, an offensive putrid smell, but less so than if air had been allowed access 



