BLOOD, MORBID CONDITIONS OF THE 



415 



deep or blackish hue, and then resembles 

 venous blood in its appearance and pro- 

 perties. 



It now became a question of the very 

 highest importance in the theory of respiration 

 to ascertain whether the oxygen acting upon 

 the blood in the manner specified, produced 

 the carbonic acid disengaged, by combining 

 directly with carbon supplied by the colouring 

 matter or some other element of the blood, 

 or whether the oxygen was simply dis- 

 solved by the blood and in dissolving ex- 

 pelled the carbonic acid which existed in it 

 ready formed. 



Various experiments satisfy us that venous 

 blood contains carbonic acid already formed. 

 My brother, Dr. W. F. Edwards, has shown 

 that those animals which possess the greatest 

 powers of resisting asphyxia continue for a 

 long time to disengage carbonic acid when 

 kept in vessels filled with pure azote or hy- 

 drogen, circumstances under which it is im- 

 possible that the carbonic acid evolved can 

 proceed from the direct combination of in- 

 spired oxygen with the carbon of the blood. 



By placing venous blood under the receiver 

 of an air-pump, several inquirers had indeed 

 already found that bubbles of carbonic acid 

 gas were disengaged from it, when the pres- 

 sure of the atmosphere was withdrawn. This 

 fact, first observed by Vogel,* has been verified 

 by Messrs. Brande, Bauer,! and others. The 

 quantity of carbonic acid disengaged in this 

 way, however, is very small, and altogether 

 inadequate to explain the phenomena accom- 

 panying respiration ; but if, after having freed 

 a quantity of blood as completely as possible 

 from its carbonic acid by means of the air- 

 pump, it be agitated with hydrogen or any 

 other gas, this will be absorbed, and a fresh 

 and corresponding disengagement of carbonic 

 acid will be determined. J On the other hand 

 there is an experiment of Girtanner, mentioned 

 by Hassenfratz, which goes to prove that 

 arterial blood contains a portion of free oxygen 

 in its constitution ; but this conclusion appears 

 to require confirmation. 



The bright vermilion or dusky red colour of 

 the blood, however, does not depend solely 

 on the nature of the gas it holds in solution, 

 or with which its colouring matter is in com- 

 bination. The recent experiments of Dr. 

 Hoffmann shew that the presence of the saline 

 matters it contains is necessary to the phe- 

 nomena in question. Blood freed from these 

 saline ingredients is black, and cannot be 

 brought to the vermilion red tint as usual by 

 the action of oxygen. The same physiologist 

 also ascertained that the presence of an over- 

 dose of saline matter in blood charged with 

 carbonic acid, equally prevented the ordinary 

 action of oxygen in changing its colour. 



The blood does not invariably exhibit the 

 properties and the mode of composition which 



* Schweigger's Journal, Bd. xi. 

 f Home, Croonian Lecture, Philos. Trans. 1818. 

 j Hoffmann, Lond. Med. Journ. May, 1828. 

 Ann. de Chimie, Here Serie, t. ix. 



we have just ascribed to it in the normal state. 

 There was a time when physicians ascribed 

 the greater number of internal maladies to 

 alterations of this fluid ; the general errone- 

 ousness of this opinion, however, was at 

 length detected, and at the present day patho- 

 logists have probably fallen into the opposite 

 extreme, namely, that of neglecting the study 

 of the changes which the blood does actually 

 undergo, although these are sufficiently striking 

 in many cases, and undoubtedly exert an im- 

 mense influence upon the animal economy. 

 A careful examination of their kinds and effects 

 were undoubtedly fraught with results of equal 

 importance in a medical as in a physiological 

 point of view. 



(H.Milne Edwards.} 



BLOOD, MORBID CONDITIONS OF 

 THE. The nature and properties of blood in 

 its normal condition having been considered in 

 the foregoing article, we proceed to notice those 

 changes to which it is liable in a state of 

 disease. 



That a fluid which is destined to receive and 

 convey materials for the formation, increase, and 

 repair of every structure in the animal frame, 

 winch carries away whatever is useless, and is 

 brought into perpetual contact with the external 

 atmosphere, should itself be subject to morbid 

 alterations, is a notion so natural, so entirely in 

 accordance with what might a priori be ex- 

 pected, that, independently of all reasoning, and 

 antecedently to all proof, it has existed in the 

 common belief of every age and of every 

 nation. 



To preserve a healthy state of the blood has 

 accordingly ever been considered an object of 

 primary importance. The greatest pains have 

 been taken to maintain its purity, as well in the 

 individual as the species ; not only in man, but 

 in all those animals which he has domesticated 

 for his use ; and there is no belief more generally 

 received than that which attributes the origin 

 of many of the cutaneous eruptions, and of 

 most of the cachectic diseases, to the degene- 

 racy and poverty of this vital stream. 



When from this general and popular notion 

 we advance to the more especial assumption 

 that the origin of all diseases is to be found in 

 the blood and other fluids ; when we classify 

 these into hot and cold, moist and dry, or into 

 blood, bile, black bile and phlegm, and attribute 

 morbid changes and even natural dispositions to 

 the prevalence of one or other of these supposed 

 humours, we quit the belief of the people to 

 follow theories far less tenable, invented at a 

 period when authoritative assertions had the 

 weight of proof, and when the dogmata of a 

 philosopher were preferred to facts plainly re- 

 corded in the book of nature. 



It would be out of place here to enter into a 

 discussion of the merits of the humoral pa- 

 thology as compared with the various doctrines 

 which have supplanted it, and to which it is 

 not unlikely that in an improved form it may 

 again succeed. 



Under the triple relation of vital phenomena, 

 intimate structure, and chemical composition, as 



