470 ////: RESPIRATORY APPARATUS l\ M.\MMM.I.\. 



gical functions of the lung, like the vena port.u with tin- liver, ;iiv very 

 properly distinguished from the other arteries or veins of the or^uii liy the 

 designation of fnn<-ti,ntnl n-am-Is. But though they arc so named, it must 

 not be inferred that they are excluded from all participation in the nets of 

 nutrition. It is now admitted by competent authorities that the blood 

 of these vessels concurs to sustain vitality in the tissue of the lun^. in 

 common with the nutritive fluid carried by the arteries and veins now to le 

 described. 



Nutrient vessels. By this name is designated the divisions of the 

 arteries and veins, whoso terminal ramifications anastomose with 

 the capillaries of the pulmonary vessels at the ultimate bronchules. 



Lymphatics. These vessels are divided into superficial and deep. The 

 first form a network beneath the pleura ; the second exist in large numbers 

 around the lobules. They mix together, and terminate in the bronchial 

 glands. (Lymphatics of very small size have been described as commencing 

 in the alveolar spaces, on leaving which they gain a proper coat or internal 

 tunic, and are subsequently supplied with valves.) 



Nerves. The nervous branches supplied to the tissue of the lung come 

 from the same source as those of the bronchial tubes the pneumogastric and 

 great sympathetic nerves. Their ramifications accompany the pulmonary 

 vessels and bronchire, and they show small ganglia on their course. 



FUNCTIONS. To know that the lung is the seat of the absorption of 

 oxygen and the expulsion of carbonic acid from the nutritive fluid 

 phenomena accompanied by the transformation of the dark into red-coloured 

 blood, and probably of several other metamorphoses yet doubtful or un- 

 known is the only authentic fact necessary to remember with regard to the 

 functions of this organ. It must be added that the subtle molecular opera- 

 tions from which all these phenomena result, take place in the lung by tho 

 mediate contact of the atmosphere introduced into the air-cells during 

 inspiration, with tho blood traversing the walls of these cells. With the 

 intimate mechanism of these molecular actions we have nothing to do here, 

 however. 



DEVELOPMENT. Although the lung is in a state of inactivity in tho 

 foetus, yet it is one of the organs early developed. During the whole period 

 of foetal existence, its lobular texture is much better defined than in the 

 adult, and it then 'appears to be formed exactly like a racemose gland. 

 Sections of it prepared for microscopical examination distinctly show the 

 vesicles and their arrangement. We have already made known tho differ- 

 ences in colour and density which distinguish the pulmonary tissue of tho 

 fuetus and that of tho adult. It only remains to repeat what has been said 

 as to the slight vascularity of the first, and to note that the blood of tho 

 pulmonary artery passes almost entirely into tho posterior aorta by the 

 arterial canal (or ductus arterionuh. 



DIFFBUEVTIAL CHARACTERS IN THE LCNG3 OF OTHER THAN 80LITED ANIMALS. 



Tho lnn;8 of tlio Or, .SV</,. and '.'</ MIT remarkable for tin- distinctness \\ilh which 

 the lobules are defined. Tlicy are, in fact, separated l>y thick layers of << llular tissue, 

 continuous with the internal face of tho visceral pleura. (These thick septa are rather 

 the interlobular raniitii-atioiin sent oil' from the xiilwruttx envelope.) Dictrichs, who as 

 the first to <lniw attention to thispc onliarity in the larger Uimiinants, has justly remarked 

 that it perfectly explains tho altogether special characters of the lesions of pneumonia in 

 tin -< animals 



The general fipure of the Inn^s of Iiiiminants does not differ from that observed in 

 tlie Morse; the left lung, however, is divided int> two lube*, and the ri^ht into four, 



