128 ASSOCIATION OF H^MATIN AND OXYGEN. 



the quantity of water they have received has distended them to their ut- 

 most capacity, they then are invisible ; but when it is withdrawn from 

 them by establishing exosmosis through the addition of saline sub- 

 stances, they may reappear in the corrugated or star shape, as seen in 

 the photograph, Fig. 50. 



With respect to the action of the hsematin, it may be observed, that 

 Action of hsem ot ^ ier nitrogenized coloring materials present a similar rela- 

 atin illustrated tion to oxygen. As an example, indigo may be mentioned, 

 by mdigo. j cons ^ er that the properties of this substance illustrate in 

 a significant manner the properties of hasmatin in the system. Indigo 

 occurs in the leaves of the plant which yields it in a yellow and soluble 

 state. It is easily extracted from them by maceration in water. Ex- 

 posed to the air, it absorbs oxygen, becomes insoluble, and simultane- 

 ously, gains a deep blue tint. So lightly is the oxygen thus united to 

 it, that by exposure to very feeble agents it surrenders it up, and repasses 

 into the yellow and soluble condition. Once more exposed to the air, 

 it turns blue, and once more may have that color removed from it by tak- 

 ing its oxygen away. For many times in succession its tint may be 

 thus changed, and made yellow or blue at pleasure. 



From this we perceive in what a loose manner oxygen is held by such 

 a coloring material ; how readily it surrenders it, and how readily it re- 

 covers it. Such a union can scarcely be called an oxidation or a com- 

 bination ; it is rather an association. 



All this is precisely what occurs in the case of hasmatin. It takes up 

 Feeble union of Ox 7g en w ^ n rapidity as it goes over the cells of the lungs, 

 oxygen and and turns scarlet ; it surrenders that oxygen with equal fa- 

 cility as it passes the systemic capillaries, and turns blue. 

 This change of color is incessantly taking place ; it is now red, and now 

 blue, as the cells are passing in the greater and the less circulation. 



Formerly it was supposed that, in the act of respiration, oxygen from 

 Eeception and the air united with carbon of the blood or of the cells, and 

 ofTx^genty car ko n i c acid formed, a combination or perfect oxidation 

 the blood-cells, taking place in the lung. But, , if this were true, the tem- 

 perature of those organs should be higher than that of the rest of the 

 body, and this is by all admitted not to be the case. 



The cells are therefore carriers of oxygen. They receive that vivify- 

 ing principle as they move over the respiratory cells, and, freighted with 

 it, pass to all parts of the body, not united with it, nor disorganized, nor 

 burnt up by it, but holding it loosely, and ready to give it up and go 

 back again for a fresh supply. * 



The sac containing the haematin offers no kind of resistance to these 

 exchanges. It will be fully demonstrated in the chapter on respiration 

 that this is the case. Thick pieces of India-rubber, stout animal mem- 



