ON THE LUNGS IN BRUTE ANIMALS. 3 
want of communication between, these lobuli. Broken wind is 
the unnatural running together of several of them. 
The Minute Lohuli. —To these lobuli we have traced the 
ramifications of the bronchial tubes, but no one has demonstrated 
their entrance into them, nor the actual structure of these minute 
and ultimate subdivisions of the substance of the lungs. There 
has been many an ingenious theory about it, and w'e have been 
favoured with one or two very pretty diagrams of the bunch-of- 
grape-like terminations of the air-tubes. They probably have 
some such termination, but we have no ocular demonstration of it. 
The Ramifications of the Bloodvessels. —An account of the 
bloodvessels of the lungs belongs to the circulatory system, but 
I may say at present that the pulmonary artery (artery we term 
it, for it proceeds from the heart, although it discharges the office 
of a vein by carrying black blood) arises from the right ventricle 
of the heart; it winds towards the root of the left lung, and there, 
at the bifurcation of the trachea, divides into two trunks, one of 
which penetrates each of the lungs. It very soon subdivides, fol¬ 
lowing the divisions of the bronchiae; it multiplies its ramifications 
as these tubes are multiplied ; and it may be traced in company 
with them to the lobules which I have just described. Some 
successful injections have enabled us to trace them further, for 
the fluid has returned by the pulmonary veins. It has traversed 
these lobules, and has been conveyed back again towards the 
heart. We do, in point of fact, find other vessels of different 
structure returning blood from the lobules. We call them veins, 
because they go to the heart; but they discharge the function of 
arteries by carrying red blood. They are minute at first; but 
they anastomose with and fall into each other, until they assume 
a decided character, and constitute the branches and the trunk 
of the pulmonary veins which empty themselves into the left 
auricle of the heart. 
The Alteration of the Blood in the Lungs.- —Gentlemen, I here 
feel the inconvenience of the plan, which, for the accommodation 
of some of you who had attended my lectures on the sensorial and 
circulatory systems, I have in the present session adopted. Many 
of you have heard nothing of the mechanism of the circulation of 
the blood, nor the changes which are effected in that fluid, as it 
traverses certain vessels or certain parts; and therefore I am 
reluctantly compelled to confine myself to the simple statement, 
that the change produced as the blood circulates through the 
capillaries of the lungs is precisely the reverse of that which 
takes place in the capillaries of the other parts of the frame. In 
the general capillary system, the blood is changed from red- to 
