126 PHYSIOLOGY. 



Loose Notes and Queries on the Blood. 



I think it is probable that not anything that is mechanically diffused 

 through the blood, can agree with it, and I conceive that it will most 

 probably kill. Thus air, milk, &c, kill in very small quantity. There- 

 fore whatever agrees with, or does no hurt [to the blood], must be in 

 solution in it, although at the same time every thing that may be in 

 solutiou may not agree with it. 



"What would be the consequence if a part of the circulating blood 

 was deprived of life, as from a part being struck with electricity? 

 But probably a part cannot be struck so as to kill the blood only ; the 

 whole must die. 



Arterial blood becoming dark in the living body by rest, as when 

 extravasated, and not in a vessel, shows its living powers. 



There appears to be a greater variety in the quantity of red blood in 

 birds than in any other known animal : some have little, others a great 

 deal. It is also thrown more on particular parts in the bird, because 

 they have two modes of progressive motion ; therefore as the one [by 

 the wings] or the other [by the legs] predominates, so is the red blood 

 thrown. 



On the Circulation. 



In many animals, especially the more perfect, the nourishment, or 

 whatever is taken into the system, is taken up and carried from the 

 stomach and other parts, by the absorbents, to an engine called the 

 heart ; from which it is thrown out into tubes which conduct it to 

 every part of the body, and thence it is again returned to the heart by 

 other vessels. 



An animal body has in general been considered under the idea of an 

 hydraulic machine, because it appears to be almost wholly composed of 

 tubes in which fluids move. I shall not at present enter into all the 

 different opinions concerning the uses of these tubes, especially of that 

 system called arteries, how they are variously affected, and how they 

 produce their various actions according to the different stimuli either of 

 health or disease ; but shall only give some general ideas of the most 

 immediate uses of the three different systems of vessels. 



The vessels in general would appear to have more powers of per- 

 fecting themselves, when injured, than any other part of the body; for 

 their use is almost immediate and constant, and it is they which per- 



ment of the arteries permitting the mixture of venous and arterial blood, as in the 

 tortoises, lizards, and lower reptiles.] 



