APPARATUS FOR PHYSIOLOGICAL USE. 259 



The interchange between the hsemoglobin of the blood and 

 the tissues is called internal respiration, because it takes 

 place quite away from the external air. It used to be sup- 

 posed that combustion took place only in the lungs. This was, 

 however, soon discovered to be erroneous, because, if so, the 

 lungs would be the furnace of the body and ought to be 

 very much hotter than any other part. This being found 

 not to be the case, people began to investigate as to the 

 part of the body in which combustion took place, and 

 found that the venous blood returning from the muscles, 

 glands, and other organs of the body contained more car- 

 bonic acid than the arterial blood distributed to them, and 

 that therefore in all probability combustion took place in the 

 organs themselves. But the question next arises whether 

 combustion takes place in the cells, of which the various 

 organs are composed, or in the small blood-vessels which 

 permeate them -1 A partial answer to this question is given by 

 the experiment which I have mentioned of the frog's muscle 

 contracting and giving off carbonic acid when no blood 

 is present, for this is sufficient to show that combustion has 

 its seat in the muscles and not in the blood. But it is very 

 probable that although the muscle gives off carbonic acid 

 as a product of the combustion which takes place in it, yet 

 that the whole of the material which is burnt in it is not 

 given out in this form. For it would appear that just as 

 in the steam engine part of the fuel undergoes imperfect 

 combustion and is passed out in the shape of cinders, 

 which may afterwards be collected and burnt, so in muscle, 

 there are certain products of imperfect combustion such 

 as sarcolactic acid and glycerine-phosphoric acid which 

 pass out into the blood and probably to some extent under- 

 go further combustion in it. But in order to ascertain 

 exactly what the changes are which go on in the muscle 

 we must have recourse to quantitative analysis, and we 

 require a more complicated apparatus, such as this instru- 

 ment which is now before you (No. 3940 in the Catalogue 

 of tlie Special Loan Collection of Scientific Apparatus, 

 third edition). It is an air-pump by which we can 

 pump out the gases from the blood. It consists of a 

 receiver (u), which contains the blood, from which the 

 gases are to be extracted, a bulb (c) filled with pumice- 

 stone soaked in sulphuric acid to dry these gases, and an 



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