524 



BLOOD. 



nature that we cannot understand even the elemen- 

 tary action of the blood, without reference to the 

 same subject in different states of the circulation ; 

 and if one of those be the healthy state, the other 

 must of necessity be a diseased one. We have it 

 indicated in tho fact that the recent blood will not 

 Jibrise (to coin a word for the sake of brevity,) if it 

 * is either too little or too much agitated ; thus we obtain 

 a sort of foundation, though not a very perfect one, for 

 our physiological consideration of the blood. 



Between these two limits, both equally fatal, and 

 varying in the case of almost every species of animal, 

 there is an average ratio of circulation which may be 

 considered as the circulation of health, and which 

 varies as much in the different races as those limits 

 between which it may be said to be the middle point. 

 The circulation in the race is always the more rapid, 

 the more active and the more continuous in action, 

 and also the more completely the organisation is de- 

 veloped ; and in the individual it rises with increased 

 action, whether external or internal, and sinks with 

 repose. It is more rapid in the young and growing 

 state than when the mature stature is attained ; and 

 those animals which are subject to short fits of very 

 violent action, with long pauses between, have cor- 

 responding differences in the action of the system of 

 the blood. 



Birds, as having to perform the most violent action 

 of any of the vertebrated animals, have the most rapid 

 circulation ; and among them the vegetable feeders, 

 which have most labour both in the finding of their 

 food, and in the assimilation of it, have the most 

 rapid circulation and the highest temperature. The 

 mammalia follow next in order, and after them the 

 reptiles, and lastly the fishes. That such is the ge- 

 neral or average distribution is true ; but there are 

 so many anomalies in all the classes, arising from the 

 adaptations of different animals of the same class to 

 different latitudes and different situations, that no 

 theory which descends to more minuteness than that 

 of a general connexion between a rapid action of the 

 system of the blood, and a corresponding activity in 

 the general habits of the animal, can be implicitly 

 depended upon. 



Something similar as to the correspondence be- 

 tween rapidity of circulation and energy of action, 

 may be traced among the invertebrated animals. Of 

 these, the winged ones have the warmest tempera- 

 ture, and thence, from the general analogy, we may 

 premise that they have the most rapid circulation ; 

 and in all cases the supply of food required is in pro- 

 portion to the circulation. Not indeed as regards 

 the quantity taken at one time ; for many of the 

 species which feed most voraciously when they do 

 feed, are capable of bearing the longest periods of 

 abstinence. The blood of the invertebrated animals 

 is, in most cases, bluish or whitish, and but rarely red ; 

 but in what respects it differs physiologically from 

 the blood of vertebrated animals, we have no satis- 

 factory means of ascertaining ; and, as we have 

 already said, chemical analysis can be supposed to 

 throw little or no light upon the action of this fluid. 



Many conjectures have been made, and many 

 theories proposed and overturned, with regard to the 

 specific action of the blood ; but the subject still 

 remains, and will probably for ever remain, involved 

 in great obscurity. There are some circumstances 

 which give at least a semblance of probability to 

 Hunter's hypothesis of "the life of the blood," that 

 is a vital action in or of the fluid itself, without a 



pre-existent cause, dependent upon or residing in any 

 organisation. This may be inferred from the facts 

 already mentioned, that the first rudimental appear- 

 ance of the germ consists of blood and blood vessels. 

 But this is not enough for the establishment of the 

 hypothesis. The blood cannot exist or act to any 

 useful purpose without the containing vessels ; and 

 therefore, though the muscular structure of the heart 

 (for the heart in all animals, of whatever class or 

 kind, is muscular) may not be formed before the blood 

 which it contains and propels, yet we cannot suppose 

 it to be formed after. Besides, though these may be 

 the first rudiments of organic structure in the young 

 animals, they are not the original germ, nor can their 

 action be regarded as the first action of the germ. 

 The germs of some animals can retain their vitality 

 for very long, and even indefinite periods of time, 

 and some of them admit of being boiled or frozen, or 

 both ; and still, under favourable circumstances, they 

 awaken into life. Towards the awakening in these 

 cases too, no further interference of an animal is re- 

 quired, so that in some of its forms, animal life can 

 lie dormant, in a very low state of organisation, (if 

 indeed we can with any propriety call eggs organised 

 bodies,) a state in which there is nothing developed 

 which we can call either blood or a blood vessel. 

 When the egg, which is the usual form of those per- 

 manent germs, is placed under favourable circum- 

 stances, the life in it begins to act; therefore we 

 might as well predicate life of the heat and humidit}', 

 or whatever other 'circumstances it may be which 

 stimulate the germ and produce the development, as 

 of the blood vessels and blood which are the results of 

 a previous action. This action is no doubt very sim- 

 ple and rudimental. But still, however simple and 

 rudimental it may be, we know that it must take 

 place ; because we have the visible results of it in the 

 vessels and the blood, and though these are the results, 

 and not the action or its cause, still all the evidence 

 which we can have of any action or any cause of ac- 

 tion, however powerful we may imagine it to be, is 

 precisely of the same description. We know, and 

 we can by possibility know nothing but results ; and 

 yet we are so constituted that we can no more sup- 

 pose any result to take place without a cause adequate 

 to its accomplishment, then we can believe any one 

 object to be at one and the same time in two different 

 places, or to be itself and at the same time another. 



Hence it is impossible for us to believe that the 

 primary and rudimental life of any animal as a germ 

 can be seated in that blood which does not begin to 

 exist till after the action of the germ and in conse- 

 quence of it ; and therefore the blood cannot be the 

 depositary of the original life ; and if we suppose that 

 it subsequently becomes endowed with a sort of or- 

 ganic vitality, we are not entitled to consider the blood 

 as exclusively or pre-eminently endowed with a vitality 

 which obviously belongs to the whole animal as an 

 organic structure. 



If the expression can be allowed, the apparent 

 vitality of the blood appears to be the result of mus- 

 cular energy, for when the heart is no longer able to 

 propel the blood, that fluid stagnates, and ceases to 

 perform its function, and life is at an end. Thus as, 

 on the one hand, what we term the life or living ac- 

 tion of the blood, takes place only consequent to a 

 previous action, so the cessation of life in the blood 

 appears to be preceded by a cessation of life in that 

 organisation, by which the blood is circulated ovei 

 the system. 



