94 



facts: 1st, in the crustaceous egg there is only a very small space, 

 which is said to contain air: it is to be proved that the air thus 

 contained, is sufficient for the oxygenation of so considerable a 

 quantity of blood as is circulated in the maturer embryon. To 

 affirm this postulatum is contrary to analogy (upon which the 

 argument on both sides is founded), for we iind in that stage of 

 Jife in which the necessity of a supply of oxygen is unequivocal 

 that no stationary or fixed quantity is sufficient; it must be per- 

 petually renewed, or its effect ceases. That this is done in the 

 chick, remains to be shewn; and it must first be discovered that 

 the egg possesses a source of air capable of compensating a per- 

 petual exhaustion. 2nd, The same, or a still greater difficulty of 

 the same kind, occurs in the human ovum, where a source of 

 oxygen is not found to have been provided. 3rd (and most con- 

 clusive), Fluids, furnishing all the elements of blood, as those con- 

 tained in the egg, as those supposed to transude through the 

 maternal portion of a placenta, or even as those contained in the 

 lacteals of an adult, may be exposed to oxygen, pure or mixed, 

 to all eternity, and will not become red blood. Oxygen therefore 

 in conjunction with nutritious fluids does not make red blood. 



77. But it is obvious that oxygen is capable of changing the 

 colour of blood; we know that exposure of venous blood to oxy- 

 gen will make it of a bright red colour, and the privation of its 

 vxygen leaves it of a still darker red. From which fact the ab- 

 surdity of imagining oxygen to be the cause of the colour in blood 

 is very manifest. 



78. Neither can we say that iron is the cause of the colorifi- 

 cation of a nutritious fluid, 1st, because there is in the egg no 

 other source of iron than that which is within itself; where, if 

 any, it remains combined with the nutritious fluid, without form- 

 ing blood (as before incubation, &c.); and, 2nd, iron mixed with 

 such nutritious fluid, as chyle, for example, whether sparingly or 

 abundantly, will not make red blood: oxygen also may be added 

 and fifty other fanciful ingredients, but nothing will make the 

 identity of red blood where there is the absence of the efficient 

 properties of the organic spirit, which otherwise, by their relations 

 with the materials, do make red blood. This is too obvious to be 

 further spoken of, though the argument may if required be very 

 much strengthened. 



79. Notwithstanding all that has been just said to detract 

 from the agency of oxygen, which some zealous admirers 

 and bad reasoners have, in a fit of enthusiasm or insanity, cried 

 up as nothing less than omnipotent and universal; notwithstand- 

 ing our restrictions, oxygen is proved, past doubt, to be capable of 

 altering the colour of blood, and of furnishing it with properties 

 which are essential to the maintenance of life. It therefore remains 

 that we should trace more closely its relations with foetal existence. 



80. It is inferred, a priori, that red blood is made by the 

 properties of the organic spirit, iu which chymical agents have no 





