Direct Observation of Capillary Circulation

Marcello MALPIGHI. From De pulmonibus epistola altera, Bononia, 1661; tr. by T. S. Hall for this volume.

To eyes otherwise attentive solely to structure and composition [i.e., of the lung—Ed.], microscopic observation reveals things even more remarkable. For, provided the heart still beats, contrary movements of the blood in the veins are (admittedly with difficulty) to be seen. By this is manifestly revealed the blood’s circulation, which is also, and even more happily, to be discerned in the mesentery and other major veins contained in the abdomen. In this way the blood pours floodlike into the smallest openings, through the arteries, and by one or another of the branches crossing through or terminating here, into each little compartment. And, by being so much subdivided, it loses its red color, and, conducted roundaboutly, is everywhere distributed until it reaches the compartmental walls and angles, and the reabsorbing brandies of the veins.

The power of the unaided eye could not be extended further in the dissected, animate living being, whence I had been led to believe that the blood’s substance was emptied into a vacant space, and, by some open pathway, was recollected by the peculiar structure of the compartmental walls, the possibility of which was attested by the blood’s motion (twisting, and pouring out in all directions) and its coming together (all toward one side). My belief was shaken, however, by dried frog’s lung which keeps its blood-redness even in the smallest little vessels (for that such was their nature was to be grasped later) where, by means of a more perfect glass, there met the eye not a skin fashioned of specks, as in what we call ’Sagrino,’ but actually small vessels attached to each other like rings. And so extensive is the subdivision of these little vessels, issuing thus from artery and vein, that the orderly arrangement proper to vessels is no longer maintained, but instead there comes into view a net, constituted by the extensions of the two sorts of vessels. Not only does the net occupy the whole empty region, but it extends also to the compartmental walls, and is augmented by the excurrent vessels, —just as I was able to observe, also, (admittedly with difficulty) in the elongated and equally membranous and transparent lung of the tortoise. Here it appeared that the subdivided blood, by this impetus, ran through twisted vessels and was not poured out into empty spaces, but was driven through little tubes and dispersed by the frequent turnings of the vessels. Nor is it uncustomary for nature to join together the open ends of the vessels, for she does the same thing in the intestines and other body regions, which will not seem more remarkable than that she should join upper termini of veins to lower ones in a visible anastomosis, as the most learned Fallopius has very well shown.