The state of or a deficiency in the quantity of circulating blood, whether induced by natural or artificial causes, is no less detri mental to health than its excess. Its symptoms are general pallor, weak circulation, languor, syncope with palpitations, oppressed respi ration, flatulency, general cedema, and, in extreme cases, effusion into all the serous cavities.
Neither plethora nor anaemia necessarily imply, though they are generally complicated with some morbid change in the blood itself. We therefore pass them over with this slight notice, referring for further information to the excellent observations of Andral, in his work on Pathological Anatomy.
The circulating blood consists essentially of a homogeneous fluid and red particles, and the former, when removed from the body or from the circulation, separates into a fluid and a solid portion. The solid, when washed and freed from the serum and red particles which are mechanically entangled in its substance, consti tutes the proximate animal principle called fibrine. The fluid contains water, albumen, oil, animal extractive, and salts, alkaline, earthy, and metallic.
With the exception of the oil and fatty matter, which, in a healthy state of the blood, do not amount to four parts in a thousand, its constituents are all heavier than water, and something is to be learned by ascertaining its specific gravity. In the information thus gained, however, we are limited to the al ternative, either that some one or more of these constituents is in a state of excess or of de ficiency, the proportion of water remaining normal, or that the water itself is either su perabundant or deficient.
The specific gravity of healthy blood has been variously stated by different authors. Haller makes it on the average 1,052 ; Blu menbach, 1,054 ; Berzelius, from 1,0527 to 1.057 ; Denis, 1,059; but none of these au thors note the temperature at which it was taken, although, from their manner of ascertain ing it, there must have been considerable variety in this respect. By experiments which I have often repeated with an accurate specific gravity bottle holding 1,000 grains of distilled water, I find that with that fluid four degrees of Fahrenheit's thermometer corresponds with a difference of •001 of specific weight, water being 1,000. Consequently, if one author states the specific gravity of blood at its circu lating temperature 98° Fahrenheit, while an other states it at 60° Fahrenheit, the usual standard, the former will make it •0095 lighter than the latter.
The heaviest blood of which I find a record among my own observations was that of a man suffering under diabetes mellitus. At a tempe rature of 87° Fahrenheit it was of specific gra vity while that of the serum was under the average standard of health, namely, at 600 Fahrenheit, and of the medium propor tion to the crassamentum, being, after twelve hours' rest, as 1000 to 1323. The specific gra
vity of the crassamentum was 1-088.
The lightest blood which I have met with was of specific gravity 1.031, at 90° Fahren heit. It was taken from the arm of a female, aged 22, who was bled on account of headach, arid had a full pulse of 117.
The red particles being the heaviest of all the constituents of the blood, their relative quantity must greatly affect its specific gravity; and as Messrs. Prevost and Dumas have shewn that they bear a general proportion to the de gree of animal heat, we might reasonably sup pose that, cateris paribus, the heaviest blood would be found in those diseases which are marked by high action and increased tempera ment. In a fluid so complicated, however, in which every constituent is liable to such variety in quantity, it is difficult to estimate the precise influence of each. I am not aware that any experiments have been made on this subject.
Blood diminishes in specific gravity in pro portion to its frequent abstraction, for the red particles and the fibrine are reproduced with more difficulty than the serum or the salts. The serum also becomes lighter from a gradual di minution of its solid contents. A recent paper by Mr. Andrews, in the fifteenth-volume of the Medical Gazette, p. 592, proves these facts very satisfactorily by experiments made on calves. They have, however,. been long known.
The specific gravity of morbid blood, says Thackrah, differs little from that of healthy blood ; but this observation is only true of an average deduced from numerous specimens of blood examined under different forms of dis ease. It would be equally true, perhaps, according to the same mode of obtaining a result, were we to affirm that the temperature of the body or the state of the pulse differed little in health and disease, since there might be as many instances of deficiency as of ex cess in heat or action. The assertion is not applicable to particular cases, and is, therefore, without value. Blood may be morbid from an undue proportion of any of its constituents, and it will be heavier or lighter than healthy blood according to the preponderance of the heavier or lighter principles. Where the spe cific weight is increased, it is generally owing to a deficiency in the proportion of water, as in the blood of cholera and diabetes ; sometimes to an increase of fibrine and red particles, as in plethora, gout, and rheumatism.