244 ^ MANUAL OF PHYSIOLOGY 



excised muscles ; and by the remarkable connection between 

 the amount of this production and the functional state of 

 those tissues. In insects the finest twigs of the tracheae, 

 through which oxygen passes to the tissues, actually end in 

 the cells ; and in luminous insects, like the glowworm, it has 

 been noticed that the phosphorescence, which is certainly 

 dependent on oxidation, begins and is most brilliant in those 

 parts of the cells of the light-producing organ that surround 

 the ends of the tracheae. 



Lymph, bile, urine, and the serous fluids contain very 

 little oxygen, but so much carbon dioxide that the pressure 

 of that gas in all of them is greater than in arterial blood, 

 while in lymph alone (taken from the large thoracic duct) 

 has it been found less than that of venous blood. And it is 

 extremely probable that lymph gathered nearer the primary 

 seats of its production (the spaces of areolar tissue) would 

 show a higher proportion of carbon dioxide. 



Strassburg found that with a pressure of carbon dioxide in 

 the arterial blood of 21 mm. of mercury, the pressure in bile 

 was 50 mm., in peritoneal fluid 58 mm., in urine 68 mm., in 

 the surface of the empty intestine 58 mm. Saliva, pan- 

 creatic juice, and milk, also contain much carbon dioxide, 

 and only a little, if any, oxygen. 



From muscle (to facilitate pumping, the muscle is minced, 

 and often warmed) no free oxygen at all can be pumped out, 

 but as much as 15 volumes per 100 of carbon dioxide, some 

 of which is free, that is, is given up to the vacuum alone, 

 while some of it is fixed, and only comes off after the addi- 

 tion of an acid, such as phosphoric acid. If the muscle be 

 left long in the pump, putrefaction begins to appear, and 

 this causes a discharge of carbon dioxide, which may last 

 indefinitely. 



Muscle may be safely taken as a type of the other tissues 

 in regard to the problems of internal respiration. It is 

 instructive, therefore, to observe that the great scarcity of 

 oxygen in the parenchymatous liquids which bathe the tissues, 

 here in the tissues themselves deepens into actual famine, 

 The inference is plain. The active tissues are greedy of 

 oxygen ; as soon as it enters the muscle it is seized and 



