Frogs, and their Contributions to Science. 133 



tion of the blood, but we do say that they furnished the 

 last fact required for the full and perfect proof of the doc- 

 trine he maintained. The actual transition of the blood 

 from the arteries to the veins was first observed by Mal- 

 pighi in the large capillaries of the web of the frog's foot. 



To sit in some window above a crowded street and 

 watch the different currents of thronging humanity beneath, 

 is attractive to most minds, merely as an exhibition 01 

 moving life. So to sit above the little world, the micro- 

 scope discloses in the transparent tissues of the frog, and 

 watch the moving blood currents through the capillaries, 

 even to unprofessional eyes, is strangely interesting. Now 

 the quick throbbing arterial wave, now the sluggish venous 

 flow, catches the eye. Now the tumbling procession of 

 globules crowd through some larger capillary, now each 

 individual globule glides along some narrow passage way, 

 in single file. Now the crimson tide stops a moment, 

 recedes, goes on, stops again like the heart beat, watched 

 by Uncle Toby. Altogether, the spectacle is one seldom 

 tiresome to the beholder. 



Our knowledge of almost all the important facts in phy- 

 siology connected with the circulation, has been obtained 

 by the study of its phenomena as exhibited in the frog. 

 Thus, for instance, that the capillary circulation is not 

 controlled by the heart's action, but depends on the nutri- 

 tive, and other chemical changes which the blood under- 

 goes in its passage along the walls of the minute capillaries. 

 Thus also was established the existence of the white cor- 

 puscles of the blood, as well as the red, and their peculiar 

 route of travel. Indeed, in no class of animals can the 

 corpuscular changes of the blood be better, or more 

 readily studied, than in the frog. Again in the true 

 appreciation of that condition of the circulation, known as 

 congestion, and its distinction from the process called 

 inflammation, about which as many vague things have 



