168 On Absorption. 



Exjperimnent 4. — Green dye produced no effect. I found 

 it unabsorbed beneath the skin. 



Having traced these colours from beneath the skin to the 

 heart in the frog, rendered it unnecessary to perform the 

 same experiments with a dog or fowl, in either of which it 

 would be more difficult and perhaps impossible to see coloured 

 blood at the centre of the circulation, through the denser 

 fibres of the heart ; whereas, in the frog, the delicate struc- 

 ture of this organ permits of the colour of the blood being 

 easily seen through it. This is a very beautiful experiment, 

 and I recommend it to the notice of physiologists as showing 

 clearly one form of absorption, and, "provided the 2^ericardium 

 be not opened, the heart's action. We have now to consider 

 by what means the dyes reach the heart. 



It has been before stated that the lymph and chyle cor- 

 puscles are readily and deeply dyed by magenta, and as by 

 injecting into the peritoneum the dye is brought into close 

 proximity to the lacteals, and hence most liable to absorption 

 by them, I performed numerous experiments upon dogs and 

 fowls, and having killed them as soon as the dyes appeared 

 in the urine, laid bare the the thoracic duct, as I had pre- 

 viously the heart in frogs, to see, its coat being transparent, if 

 its contents, the chyle, were coloured. 



In no instance could I detect the colour of the dye used, 

 either in the thoracic duct, lacteals, or lymphatics. 



It is reasonable to suppose that had the dyes been absorbed 

 by the lymphatics and lacteals, and not by the veins, they 

 would have been as readily seen in the thoracic duct as they 

 had previously been in the frog's heart, or even more 

 plainly. 



Leaving for the present what I have to say of the blood, 

 I pass to the microscopic examination of the other fluids and 

 tissues. 



I have already mentioned the dyes employed, and it 

 only remains to state, that they were of all degrees of 

 concentration, from their undiluted condition to the propor- 

 tion of one part of dye to twenty of water. Generally they 

 were injected into the peritoneal cavity, or beneath the skin, 

 and once into the cavity of the pleura. Sometimes their 

 temperature was raised to that of the blood of the animal ; 

 at other times they were injected cold. The dye usually 

 appeared in the urine a few minutes after injection, and 

 half an ounce of the dye — a quantity sufficient to make a 

 gallon of ordinary dye — passed entirely out of the body in 



