92 The Functions of the Blood. 



the muscular juice, iu respect even of some of the most diffu- 

 sible substances. Thus common salt, an extremely diffusible 

 compound, is found in large quantity in the blood, but is almost 

 entirely absent in muscular juice, and the blood is invariably 

 and necessarily alkaline ; whereas the liquid of the tissue is acid, 

 and may even contain, as Liebig has remarked, enough acid to 

 neutralize the blood. Probably the pressure under which the 

 blood flows, influences in some manner the exudation, but it 

 would be vain to pretend that it explains it.* 



The excess of the nutrient fluid, together with the products 

 of the disintegration of the tissues, returns to the blood, a 

 portion perhaps direct to the capillaries, but the great bulk, in 

 all probability, through the lymphatics, which seem to act as 

 overflow-pipes to the tissues. Mayer therefore suggested that 

 the quantity of lymph might be taken as a measure of the 

 quantity of fluid exuded in a given time. Bidder and Schmidt 

 estimate the lymph returned to the blood in twenty-four hours 

 at 22 lbs., but it is safer to assume it to be at least 30 lbs. It 

 would hardly do, however, to take even this quantity as a 

 representation of the average exudation through the capillary 

 walls in twenty-four hours, and I have thought it right to 

 treble it, so as to have a decided over-statement of its probable 

 quantity. We thus get 90 lbs. a day, or about 40 litres. Now 

 if oxygen leaves the blood and passes into the tissues, it is 

 evident that it must pass in solution in this 40 litres of exudate. 

 How much oxygen could possibly be dissolved by this 40 litres ? 

 There is every reason to believe that the exudate does not 

 differ materially from liquor-sanguinis in composition, and we 

 have before seen that liquor-sanguinis is about equal to 

 water in its power of dissolving oxygen. 40 litres of water 

 would dissolve less than two grammes of oxygen ; and 

 this quantity of oxygen, whether it were employed in the 

 oxidation of muscle, of fat, or of sugar, could not yield as 

 much as 3000 metre-kilogrammesf of force. But it may be 

 urged that, though unlikely, it is still possible that the exuding 

 fluid may be able to carry with it a larger proportion of oxygen 

 than this. Be it so. Let us make the absurd assumption 

 that every hundred volumes of exudate contains more oxygen 

 than the arterial corpuscles themselves do, when saturated 

 with the gas. If each hundred volumes of exudate con- 

 tained forty volumes of oxygen, 40 litres would still only 

 contain about 23 grammes, and this, in uniting with oxidizable 



* Some of these arguments were suggested to me by Dr. Marcet, F.R.S., who 

 has studied the bearings of dialysis on pathology with great care and success. 



f A metre-kilogramme is the force required to raise one kilogramme one 

 metre. It is equal to about 7i foot-pounds, and is now almost universally 

 employed as the measure of force. 





