636 THE POPULAR SCIENCE MONTHLY. 



are, and the only difference to be noted in this respect is that the pro- 

 cess takes place within the very plasma itself, while the other elements 

 are parted from it by the thin membrane of the capillary vessels. The 

 o-lobule has so distinct an existence of its own, that the chemical prin- 

 ciples composing it are not found in its plasmatic medium. The va- 

 rious reactions shown by these little bodies in presence of chemical 

 agents lead to the belief that they are found in the plasma in all 

 stages of their development ; their dimensions are not the same at the 

 different ages of our organization. When the human germ is in pro- 

 cess of evolution, the first lineaments of the vessels are traced in the 

 depths of the tissues, and the heart begins to beat ; the sanguine fluid 

 is then formed, but the globules it contains are much larger than they 

 will be after birth and in adult age. During this embryonic life the 

 newly-formed blood does not communicate with the vessels in the 

 maternal system the two circulations being juxtaposed, but indepen- 

 dent ; there is not, as the belief in the seventeenth century was, a natu- 

 ral transfusion of the mother's blood into that of the embryo, because 

 the solid particles or globules of each circulate and remain in each 

 of unequal size. The study of the blood-elements in the animal series 

 is interesting ; they are found larger in fish and reptiles than in birds 

 and mammals, whose vital activity depends on other powers. In spite 

 of the resemblances presented by the sanguine fluid in these different 

 groups, the blood of a fish could not vivify the body of a reptile for 

 any length of time, nor could a bird's blood be substituted for a mam- 

 mal's. The animal species whose nutritive fluid is mutually transfused 

 must be closely related as regards natural classification : the globule 

 which emigrates into a foreign medium can only become acclimated 

 there in so far as its conditions of existence are not profoundly modi- 

 fied. * 



The blood-globule not only lives its individual life within the 

 plasma, but it needs, in order to complete its function of vivifying 

 every part of the body, to absorb oxygen from the air, and it then 

 takes that bright vermilion color which is characteristic. The phe- 

 nomenon of that new coloring is an essentially vital act, a chemical 

 reaction taking place between two bodies, one solid, the other gaseous. 

 Precisely the same thing happens with the commonest copper coin 

 placed in contact with the air it absorbs a gas, and its surface is 

 soon covered by a colored product. In the lower animals that have 

 copper in their blood, the vine parasite, for instance, the globules take 

 a bluish color on contact with air. The same phenomenon is remarked 

 in the vegetable kingdom ; indigo, which is white in the plant, turns 

 blue when exposed to the air, and many coloring substances are 

 formed in the same way. The red globule contains iron, and the chem- 

 ical action taking place in it may perhaps be compared to the forma- 

 tion of rust. Exposed to atmospheric air, it takes a dark-red color, 

 while continuing crimson in the arteries. Deep in the tissues, the 



